Non units can't be damaged by the Firebreather's fire attack or the Chander's vomit
Making them extremely bad at dealing with anything a non-living creature. They can't even knock enemy doors at a decent pace as other creatures. And bad assaliants for the Dungeon Core.
If the thread on the forums is right, it is works only on heavily wounded units. It doesn't specify how much health does it need to lose to be affected, but still, damage amplification on already succumbing creatures is kinda pointless, it's almost like having an ability to instantly kill any creature... but only if it has less than 50 HP.
"In generall, I do not dislike that Units casts non-usefull Abilities onto Things, because they will level up" -- but they also waste so much time doing this pointless thing, I don't even.