Thihleziss the Assassin

{x}{t}: Stealth - Counter target spell or ability that
targets Thihleziss the Assassin, where X equals
the mana cost of the spell or ability. Thihleziss
the Assassin gains hexproof until the beginning
of combat on your next turn. You may {t} to
activate this ability at the end of your combat
phase if Thihleziss did not attack this turn.
If Thihleziss the Assassin began the turn with
Stealth, he gains first strike and deathtouch until
end of turn.