There's an old bug that allows you to cancel the flight altitude and time limits for dropping Ivy's airdrop bomb (called the IAC trajectory).
But with the new changes to the airdrop cast time, when you cast the ability on an ally and use the IAC trajectory, you cancel the flight altitude and...
For some reason, when you use the parry from Counterspell on walkers, it activates the parry effect; even the stun from their stomp cancels the damage, but not the stun itself.