Cheapest priced copy (Shadows over Innistrad): $0.35 at Card Kingdom, near mint, their price list as of .
Reaper of Flight Moonsilver 
Creature — Angel · 3/3 · Uncommon · Shadows over Innistrad · #36
Flying
Delirium — Sacrifice another creature: This creature gets +2/+1 until end of turn. Activate only if there are four or more card types among cards in your graveyard.
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
1 printing · $0.35 to $0.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Shadows over Innistrad | 36 | Uncommon | $0.35 | $0.49 |
5 rulings from Wizards of the Coast
- 8 April 2016Some delirium abilities are activated abilities of permanents. To activate such an ability, there must be four or more card types among cards in your graveyard. The number of card types is not rechecked as the ability resolves.
- 8 April 2016The card types in Magic are artifact, battle, creature, enchantment, instant, kindred, land, planeswalker, and sorcery. Supertypes (such as legendary and basic) and subtypes (such as Human and Equipment) are not counted.
- 8 April 2016In some rare cases, you can have a token or a copy of a spell in your graveyard at the moment that an object's delirium ability counts the card types among cards in your graveyard, before that token or copy ceases to exist. Because tokens and copies of spells are not cards, even if they are copies of cards, their types will never be counted.
- 8 April 2016The number of card types matters, not the number of cards. For example, Wicker Witch (an artifact creature) along with Catalog (an instant) and Chaplain's Blessing (a sorcery) will enable delirium.
- 8 April 2016Because you consider only the characteristics of a double-faced card's front face while it's not on the battlefield, the types of its back face won't be counted for delirium.