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.
Demonic Spiders: The enemy general's squad can turn into this if you are fighting them with a unit that they're strong against. Often your best bet is to simply run away and let your allies deal with them, or find a unit that they're weak against and take control of them.
Ear Worm: Most of the music is pretty good at evoking the emotions of the scene. For example, the music at the tavern is relaxing, while in combat the action music can get you pumped up for combat.
Game Breaker: When a friendly group of soldiers (usually 2-3 squads) are moving towards an enemy base, if you take over the units that don't have a shield icon on them while they're near their town of origin, you will spawn a new batch of troops. Can be useful if you want to try and get a unit type you prefer, or one that's strong against units in the defending town, or just simply want a larger force to attack the town with. However, doing this too much will slow the game down considerably, so you should probably only use it 2-3 times at most.
Goddamn Bats: Usually played straight when you run into a group, or several groups, of enemy units that your currently controlled squad is weak against, such as running into axe men while controlling sword troops. Or more likely, archers while controlling mounted units.