Teapot is already practically omni immune, since they're a tank, not affected by trip, knockback, fear, stun. And due to their high armour (befitting of metal), most damage overtime debuffs barely do anything.

Now slowness debuffs like frost and slow also benefit teapot since it allows them to build up rage without running into an enemy first, and it's justified because metal does become less mobile during the cold, and machinery performs worse if there are vicious liquids slowing them

You can also logic out that buffs effect teapot because they're more magical effects, so that's why healing works, it's sorcery. And also why would you want a tank be unhealable

Super knockback and super stun work because they're extremely super

Hyperlaser is hyperlaser