Common Soul Gem

Soul Trap — Whenever a creature with
power 6 or less dies, you may tap and
sacrifice this artifact. If you do, you may
search your library for an Enchantment with
mana value less than or equal to that
creature's power and cast it without paying its
mana cost, then shuffle your library. You may
not activate Soul Trap with another Soul Gem
for this creature on this turn.