[Taqwus]

Iron Dragons are flying, unbreakable tramplers... but if memory serves, there MR is not that high for the research level, and you still aren't allowed to do a flying body slam.

The whole "doesn't use its other attacks" bit is why I rarely build Boots of the Behemoth or the Stymphalian Wings.


(Edit: addition)
In addition, aye, it's pretty true that pretty much anything can be stopped by something. That counter may require much research or luck, and there are sometimes balance issues (see the arguments regarding Helheim/Vanheim in blitzes, the extremely high utility of lifedraining weapons and quickness boots in the previous iteration), but the game isn't really designed among nigh-unstoppable superunits.

Not like you've got just a platoon of M4A3s staring across a 2km open plain versus a hull-down Jagdtiger which is already positioned to aim at a bridge you've been ordered to cross. Even a lowly Flagellant has a slight chance to cause some lasting pain... especially if it's D9 or B9 blessed, and the target's defense has been lowered by swarming and fatigue (or better, paralysis).

Even a Tartarian Titan with Magebane + Aegis will be, at a minimum, paralyzed by a Petrify spell, or sent to Inferno with the Infernal Sword, or seriously wounded if hit by Gifts from Heaven, or taking unstoppable damage from Dust to Dust or Wither Bones, or so forth. There are ugly situations, some potentially quite unfair (Ancient Presence event smacking capital or getting 2x 3000-gold + magic items events early might also be huge) but there's normally more than one possible counter rather than a strict hierarchy of tactics or anything unbeatable.