Quest for the Holy Relic

Whenever you cast a creature spell, you may put a quest counter on this enchantment.
Remove five quest counters from this enchantment and sacrifice it: Search your library for an Equipment card, put it onto the battlefield, attach it to a creature you control, then shuffle.

The List

Zendikar

Whenever you cast a creature spell, you may put a quest counter on Quest for the Holy Relic.
Remove five quest counters from Quest for the Holy Relic and sacrifice it: Search your library for an Equipment card, put it onto the battlefield, and attach it to a creature you control. Then shuffle your library.

If you cast a creature spell, Quest for the Holy Relic’s triggered ability triggers and goes on the stack on top of it. The triggered ability will resolve before the spell does.

The activated ability doesn’t target the creature the Equipment will be attached to. It may be attached to a creature with shroud, for example. You don’t choose which creature it will be attached to until you actually attach it. Once you choose which creature to attach it to, it’s too late for players to respond.

You may activate Quest for the Holy Relic’s activated ability even if you control no creatures, or you control no creatures that can be equipped. In that case, you’ll simply put the Equipment card you find onto the battlefield without attaching it to anything.