Explotan, The Notorious

Whenever Explotan, The Notorious deals combat damage to a player, put a Stealth counter on Explotan, The Notorious.
{3}{u}{t}: Search target opponent's hand and
graveyard for an instant or sorcery card with
converted mana cost X or less, where X is the
number of Stealth Counters on Explotan. You
may cast that card without paying its mana cost.