Echoing hoofbeats can no longer be assumed to be help from the Gavony Riders.

Stallion of Ashmouth

Delirium — {1}{B}: This creature gets +1/+1 until end of turn. Activate only if there are four or more card types among cards in your graveyard.

The List

Shadows over Innistrad

Delirium — {1}{B}: Stallion of Ashmouth gets +1/+1 until end of turn. Activate this ability only if there are four or more card types among cards in your graveyard.

Because 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.

In 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.

Some 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.

The 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.

The 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.