austere summit
Theres basically no spell that directly affects heavy units, and i feel like if you're playing a heavy deck youll use the healing wisp or something but thats single unit. maybe a spell that would temporarily increase all heavy units armor by like 0.5% of their total hp. So for juggerknights, they would take 2.5 less damage (however the game rounds), and for max giants they would take 7.25 less damage. But just temporarily, it could also slow units down like a turtle mode
frosty edge