These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Cliché Storm: The Russian remake plays to every — and we mean each and every — fantasy cliche imaginable. Of course, it's quite intentional, and a part of the developer's signature style, but sometimes the cheesiness may get too over-the-top.
Demonic Spiders: Pretty much anything that can poison or burn opponents, both of which deal a nasty amount of damage every turn and also reduce attack and defense, respectively.
Dragons. A single dragon can cause you a lot of trouble when faced in battle. On the other hand they become GameBreakers when you can hire them in your army. If you face something like 7 Black Dragons at once, get ready to lose some troops.
Necromancers in Legend. They're fairly hard to kill without Priests or Inquisitors, often come in relatively large numbers, and they like to Plague everything on the battlefield at once and Magic Shackle your units so they can't use abilities. Their basic attack deals splash damage to everything next to their target and Curses everything it hits. They're Undead which makes them immune to a lot of things and they can revive any destroyed undead unit on the field, including each other. In order for them to stay down you pretty much have to kill every stack of them at once.
Ear Worm: The traveling theme from the original. It does not leave your head!
Evil Is Sexy: Demonesses aka Succubi. They are one of the few units in the game with the Beauty attribute, which gives them a chance to dodge against male humanoids, which they can also seduce.
Getting a Call of the Colossus scroll early in Armored Princess, especially if it creates a troll.
Hypnotize + Sacrifice in Legend and its sequels. Sacrifice allows you to do massive damage to one unit you control in exchange for permanent reinforcements to another unit, which last outside the battle; it's nearly a gamebreaker on its own, since it lets you sacrifice cheap peasant hitpoints to gain new recruits of unit types that might otherwise be available in limited supply. But guess what you can do when you combine it with Hypnotize? The weird thing is that Sacrifice won't let you sacrifice summoned units, but hypnotizing the enemy and sacrificing them works fine.
Goddamn Bats: Whenever you run into a bunch of more than 200 fairies or skeleton archers or any other annoying critter.
That One Boss: The Spider Queen. You can't use the Box of Rage and have to fight and kill a huge monster with great attack, 25000 life points and capable of summoning hordes of smaller spiders at will. To cup it all, the monster always counterattack when hit in melee and can switch place in the middle of the battle, forcing you to move around a lot to get her.
Unwinnable by Insanity: The original has an area which can only be reached by flight, and which contains only a single treasure spot. If said treasure spot contains non-flying creatures, and you were to recruit them and then ditch your flying creatures, and you didn't have any Town Gate or Castle Gate spells, you would be stuck there forever.