Mindsparker

Creature — Elemental

First strike (This creature deals combat damage before creatures without first strike.)

Whenever an opponent casts a white or blue instant or sorcery spell, this creature deals 2 damage to that player.

Mindsparker's last ability resolves before the spell that caused it to trigger. It resolves even if that spell is countered or otherwise leaves the stack without resolving.
If an opponent casts a spell that's both white and blue, Mindsparker's last ability triggers only once.