The only other cards that does this are infernal chain and Santa, and it seems a really fun mechanic. I'd love to see more instances of this.
Here are some example ideas:
Better Boots (Arcane):
Fire Affinity: ground units in a 5m radius gain swift
Frost Affinity: ground units in a 5m gain steadfast
Master Surgeon (Medium Unit) :
Nature Affinity: Every 5 seconds gives a unit that does not have it, the medically trained ability (2% life regen)
Shadow Affinity: every 5 seconds gives a unit that does not have it, the lifeleacher ability (10% life steal)
Reforge (ultra-rare) :
Give target unit the one-time ability to fuse with another unit, giving the first unit the second units abilities, while killing the second one.
Armor Spikes (Arcane):
Causes the targeted unit to gain armor spikes: reflect 20% of melee damage back at the attacker.
Edited: Santa also adds card abilities! thanks for pointing that out 😄
callsignhusker liked a post in a topic by Reloasd in Cards that give units abilities