an enchantment

Changeling (This card is every creature type at all times.)

Whenever an enchantment enters or leaves the battlefield under your control, put an Enchantment counter on an enchantment.

Remove 4 Enchantment counters from an enchantment: Reveal cards from the top of your library until you reveal an enchantment card. Put that card onto your battlefield. Put the rest on the bottom of your library in any order.