Gremlin Towers are odd units all-around, with lots of special-casing effects, so many I'm quite certain I'm not actually aware of the full list. The game also doesn't provide much information when you right-click on them, just their current and max Health, which makes it even more of a pain to figure this stuff out, which is further compounded by how they don't actually have rigid stats in the first place. In addition to the obvious Health variability, their Initiative varies (And annoyingly even if you use Alt to activate the turn order display it won't include them for calculating turn order, not even by having a conspicuous gap in the turn order on the regular units), the Evil Gremlin's damage on their retaliation varies, and the strength of their spells vary, both in terms of the Spell's actual Level and also in terms of the Intellect-style boost they get.
That said, their Magic resistance is 80%, and they have 20% Poison resistance, with no protection against Fire, Physical, or Astral damage.
In The Legend, their Health is derived by totaling up the Health of the non-Gremlin units in the Keeper fight, applying a multiplier to that total, and there you go. This means fragile units lead to fragile Gremlins. (Ironically, this means fights against higher-end units often have relatively easily-killed Gremlins) The multiplier is based on the Item Level the fight is attached to -in the case of suppressing a rebelling Item, that's of course the Item's current Level, but when upgrading an Item it's instead based on the Level you're upgrading to. As there's no in-game way to see what Level you're upgrading to, this can make for a nasty surprise, because some Item upgrades jump multiple Levels at once!
As for what these multipliers are, they're...
10% for Level 1
12.5% for Level 2
15% for Level 3
17.5% for Level 4
20% for Level 5
So in The Legend, a Level 5 Item has its Gremlins have twice the Health of a Level 1 Item if the Health of the non-Gremlins has the same total in both fights. In actuality higher-Level Items have bigger armies, but still.
In Armored Princess, Warriors of the North, and Dark Side, Gremlin Health still derives from the Health total of the non-Gremlins, but it no longer uses Item Level as a factor. Instead, it halves the total Health, and then splits the resulting number up among the Gremlins -if you have two Gremlin battlegroups with similar unit types and numbers, but one has 3 Gremlins and the other 5, the 5 Gremlins will have less Health than the 3 Gremlins. This noticeably reduces how much Gremlin Health can be on the field at max; an Item Level 5 fight in The Legend with 20,000 non-Gremlin Health on the field with 5 Gremlins would be 4,000 Health per Gremlin. In Armored princess, it would instead be 2,000 Health per Gremlin. Conversely, it makes Gremlin count less dominating of fight difficulty; take the prior numbers but switch to 3 Gremlins, and in The Legend you drop from 20,000 Gremlin Health total to 12,000, whereas in Armored Princess its total of 10,000 gets redistributed so the individual Gremlins have 3,333 (Give or take a point) Health. It's much more consistent of a result and I very much appreciate it.
In all games, Gremlins scale their Defense, Intellect, and Initiative to Item Level. For Intellect, they get 7 per Level, meaning a maximum of 35 Intellect -notably, the player's Intellect peak overall rises with each game, so Level 5 Gremlins in The Legend are only a little behind an endgame Mage, whereas in Dark Side Daert looks down his nose upon a meager 35 Intellect long before he reaches his endgame.
Defense-wise, Evil Gremlins gain 5 per Level (So 25 at most) while Friendly Gremlins gain 3 per Level. (So 15 at most) Pointing your units at Friendly Gremlins is thus a bit more effective than pointing them at Evil Gremlins, so consider pointing Spells and Rage at Evil Gremlins and units at Friendly Gremlins if you can.
Initiative-wise, Friendly Gremlins have 5 base Initiative and Evil Gremlins have 3 base Initiative -except they add the Item's Level to that, so the lowest you'll see is 6 and 4. And almost no Level 1 Keeper fights exist in the series, so you might as well treat them as starting from 7 and 5, which is kind of nuts! And of course for Level 5 Items, that's an absurd 10 and 8 Initiative, a nightmare to get the jump on. (For one thing, Black Dragons lowering enemy Initiative doesn't affect Gremlins!)
Oddly, base Armored Princess switched the Evil/Friendly Initiatives, but then Crossworlds switched them back, and Warriors of the North and Dark Side stuck to the above.
Evil Gremlins are fairly straightforward. They're basically a player-type caster except they ignore Mana and are trapped within turn order like a regular unit. The only caveat to this is that their counter-attack, though it appears to be a Lightning Spell, is actually a weak Magic damage attack with no special effects. (ie it won't bounce or Shock enemies, and on the flipside it can hurt Black Dragons, albeit only barely since it's weak and they're so resistant to the Magic damage type) Their Spell list is primarily aggressively oriented, aside from inexplicably having Divine Armor mixed in. (I guess to ensure they can do something, even if you do something gimmicky like only bring a Black Dragon stack?) The rest of it is Weakness, Doom, Sheep, Lightning, Fireball, and Pygmy. For whatever reason, they're a lot more aggressive about using Fireball in The Legend than in later games. Also note that they're strangely prone to Dooming and then Sheeping a unit -since Sheep clears all other buffs and debuffs, this wastes the Doom. So depending on AI silliness, you can end up with 4 Evil Gremlins accomplishing no more than 2 could do. This can even be exploited deliberately, such as by having Royal Thorns generate Thorn Hunters/Warriors, which surprisingly will often distract the Evil Gremlins into the Doom+Sheep wastefulness, instead of dropping Fireballs on the pair like you might expect. (Assuming you don't have other units clumped nearby: Fireball-slinging is far more likely when you have 3 or more units close enough to all be caught by a Fireball)
Friendly Gremlins are a bit odder. Firstly, their counter-'attack' is a non-damaging push, comparable to the Archmage's Telekinesis. This is mostly significant due to their second oddity: in addition to a proper Spell list, they can generate additional copies of any stack their team started the battle with, directly adjacent to themselves. They actually have to have a free space for this: if you block off all the tiles adjacent to them, they'll be unable to summon new stacks. The amount summoned is derived from the Friendly Gremlin's max Health; in The Legend, they summon a stack with roughly 33% of their max Health ('Roughly' because the stack is fully healthy; they won't summon a stack where the top member is missing 1/3rd of its Health to get the number exactly right), while in all later games they summon a stack whose Health is randomly from 62.5% of their max Health to 125% of their max Health, making this unit-summoning effect a lot more relevant past The Legend. Their proper Spell list is mostly oriented toward supporting their allies: they can cast Resurrect, Haste, and the atypically aggressive Slow spell.
Spell Level is odd. Friendly Gremlins always cast Haste and Slow at Level 3, Evil Gremlins always cast Weakness at Level 1, while the remaining Gremlin Spells have their Level determined by the Item Level: Spell Level 1 for Item Levels 1 and 2, Spell Level 2 for Item Levels 3 and 4, and Spell Level 3 for Item Level 5. This for one thing means Keeper fights have a fairly jagged difficulty curve -you can have two Keeper fights, one of which is maybe 20% more units, but which is vastly more difficult than the other because the Gremlins have leveled their spells and boosted their Intellect.
That said, Evil Gremlins are affected more by this overall, as Friendly Gremlins summoning new stacks is not affected by their spell level and Friendly Gremlins are quite fond of summoning stacks, in addition to Resurrect being their only Spell that levels and their only Spell substantially affected by Intellect. I personally tend to prioritize Evil Gremlins in general, but these facts make it even more true the higher the Item Level is.
It should be pointed out that Gremlin casting, though partially randomized, does have some sensible rules to it, where for example Friendly Gremlins won't bother to cast Haste unless a good portion of their troops are melee units who can't currently reach any of your units. The rules aren't perfect (See prior Doom+Sheep commentary), but still. For one thing, don't expect save/load usage to significantly change their behavior if you don't like what they do on the first turn.
Some oddities of Gremlins as a whole:
-You can't Fly over a Gremlin Tower as long as the unit lives. This is one of their more bizarre quirks, as no unit or battlefield object shares it. It usually doesn't even matter, but there's edge cases where it can cause problems for you. Lina's Gizmo is perfectly able to hover over them, surprisingly... which is frustrating, because its side effects are useless against Gremlin Towers, and it's perfectly happy to waste one of its attacks on a Gremlin Tower.
-Gremlin Towers are immune to almost all buffs and debuffs... but can be Poisoned and Burned. I don't really get that one, and their susceptibility to Poisoning and Burning goes away in later games. Not that it matters, since Poisoning and Burn do so little damage in The Legend, and in all later games they are immune to them. (As well as Freezing and Bleeding once those become damaging statuses) This immunity to buffs/debuffs has a bunch of implications, such as it being impossible to take control of them.
-Gremlin Towers are in many ways considered to be battlefield objects. This includes that Siege Gun provides a damage bonus against them (And honestly this is the only reason that Ability even really matters) and also means that a number of effects you might hope to use on them don't work. (eg Soul Draining and Rage Draining can't affect them)
-It's completely impossible to move a Gremlin Tower. You can't use Infernal Exchange on them, and effects like Cyclops' Push Talent or Emerald Green Dragon's Target Capture Talent will either not allow you to target them in the first place or will fail to move them while inflicting damage. (This probably ties back into the battlefield object point, admittedly, but is worth separate commentary regardless)
-Attacking Gremlin Towers does not generate Rage. (This is only true in The Legend: in later games, Rage absolutely is generated by attacking them, making them much less hostile to the Rage-specialized class)
-Generally speaking, effects that can target Gremlin Towers will prioritize them outright. The Geyser Spell, for example, will only ever hit non-Gremlin units if it's generating more geysers than there are Gremlin Towers currently on the battlefield. As alluded to earlier, Lina's Gizmo likes to prioritize them, even though they're bad targets for it. That kind of thing. It's not some absolute rule, but it's widespread enough that it makes for a good rule of thumb if you don't already know for a specific case.
-Gremlin Towers don't interact with Action Points. You can't steal them to cause them to skip a turn, or reduce their Speed to delay their turn order. (Hence part of why Gizmo targeting them is frustrating) Indeed, you can't effect their Initiative/turn position in any way: all of the Evil Gremlin Towers will always go back to back, and all the Friendly Gremlin Towers will always go back to back. There's no way to cause a Gremlin Tower to act earlier or later than the rest of its kind of Gremlin Tower. (Obvious example: you can see Shock being inflicted in The Legend, but it won't do anything) By a similar token, they can't Wait or Defend; if they can't do anything when their turn rolls around, they do nothing. (eg a Friendly Gremlin Tower you block in, with all your units being immune to Spells and no regular units on the enemy's team... it won't summon in new allies if, partway through the turn after its original turn opportunity, you move units so it has space available)
-Nonetheless, they seem to be treated by the game as having the default Speed value of 2. (As we'll see later, this gets used on Ice Orbs even though they don't use Speed for any purpose except turn order calculation. I'm fairly sure 2 Speed really is just the game's default value, if nothing was specifically entered) This matters for turn calculation reasons (Two units in the same Initiative tier may have one go ahead of the Gremlins because it's Speed 3 while the other goes after them because it's slower), but also crops up for certain specific interaction cases. (eg in Orcs on the March Veteran Orcs get an Ability that prevents retaliations if their Speed is higher than their target's Speed. They need 3 or more Speed to not be retaliated by Gremlins)
-In The Legend in specific, Gremlin Towers are, for certain purposes, considered hostile to everybody: if an enemy Sea Dog uses Fury Attack with a Gremlin Tower within the strike zone, they'll hit it. If a Cerberus attacks one of your units with a Gremlin Tower in their strike zone, they'll hit it. Even though in both cases they don't have friendly fire! This isn't super-exploitable, but it's worth keeping in mind when it can crop up. (ie it can be a good idea to move a unit adjacent to a Gremlin Tower if you expect the enemy to target them with splash damage, even if said splash damage doesn't affect allies) Thankfully later games fix this bit of jank.
-Some Talents just can't target Gremlin Towers for no obvious reason. (The one I remember off the top of my head is actually an Armored Princess-onward example: Executioners can't Execute Gremlin Towers. This is just a regular attack, slightly stronger than usual, with special benefits if it finishes off the stack, so it's pretty weird it can't target Gremlin Towers)
-Gremlin Towers don't interact with racial/factional stuff at all. This mostly doesn't matter in The Legend, but in later games you can see stuff like a Keeper fight where Elven forces are getting a mono-racial bonus even though there's Gremlin Towers still standing.
-As far as I can tell, Gremlin Towers seem to be treated as if their Level and Leadership is whatever makes them 'win' an interaction. Effects that fail on Level 5 units will fail on them (Even if an equivalent effect that doesn't care about Level does work on them), yet effects that target Level 5 units won't apply to them. (eg in later games Furious Goblins get bonus damage against Level 5 units) I'm... less certain of the Leadership point, as I'm not sure there's a case where Leadership is a factor that isn't being overruled by some other consideration (eg in Warriors of the North, Warrior Maidens won't be retaliated if the target's Leadership is low enough... and its Level is low enough. They always get retaliated by Gremlins, but this may well just be the Level favorability thing. Similarly, a lot of effects that are capped by Leadership, such as Mind Control/Charm/Magic Shackles, couldn't be applied to them regardless of what their Leadership is treated as due to their immunity to status effects), but I suspect it's true and that I'm just not remembering an example of it clearly cropping up.
Not-technically-Gremlins is the point that Keeper fights are abnormal in general. Diplomacy can't trigger on a Keeper fight, for example, and this kind of pre-battle effect becomes more common in later games, with almost all of them being barred from applying in a Keeper fight. (eg Diversions/Preparations in Warriors of the North and Dark Side) This means Keeper fights have an additional layer of difficulty, above and beyond the presence of Gremlins, which can have a pronounced impact if you're used to leaning on such effects.
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I'm not gong to be covering Gremlins in the later games. They don't change enough to justify going over them anew for each individual game, and what differences are of relevance will tend to crop up in talking about other units and the like. (ie the Trapper Medal can't trigger in Keeper fights, but I'll be explicitly covering that when covering the Medal itself. Though I suppose that brings up an example that wouldn't crop up normally in my analysis itself: the Trap Item also can't trigger in a Keeper fight)
The only particularly significant point worth noting is that when Ice damage shows up, it's not resisted by Gremlins at all, just like Physical, Fire, and Astral damage. This is most significant for the fact that a few Magic damage units switch to Ice damage, abruptly spiking their effectiveness in Keeper fights.
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Next time, we get started on Spell analysis, starting with Chaos Magic.
See you then.