Could there be an undermine variant? something like:
UU(U/B)
Instant ( (U/B) can be paid with U or B .) Counter target spell.
if any B was spent to play this spell, target player loses three life.
Or maybe a mill variant:
UUU
Instant
Counter target spell. It's controller puts the top 2 cards of their library into their graveyard.
Or a discard:
UUB
Instant
Counter target spell. If it's countered this way return it to it's owner's hand instead of that player’s graveyard. then it's controller discards a card from their hand.
UU(U/B)
Instant
( (U/B) can be paid with U or B .)
Counter target spell.
if any B was spent to play this spell, target player loses three life.
Or maybe a mill variant:
UUU
Instant
Counter target spell. It's controller puts the top 2 cards of their library into their graveyard.
Or a discard:
UUB
Instant
Counter target spell. If it's countered this way return it to it's owner's hand instead of that player’s graveyard. then it's controller discards a card from their hand.