If the controller of the target spell pays {X}, the spell won’t be countered. Mindswipe will still deal damage to that player.
20-09-2014
wotc
If the target spell is an illegal target as Mindswipe tries to resolve (perhaps because it was countered by another spell or ability), Mindswipe won’t resolve and none of its effects will happen. No damage will be dealt.
Random a card of Magic: The Gathering (MTG), but you can also roll the D20 dice, random a Planeswalker, have fun with the random rules and more.