Eldrazi Horror is one of those cards players keep asking about. Here is, in plain words, what its official text says, the rulings published by Wizards of the Coast, and the combos players actually run.

How it works : Eldrazi Horror

Original English text — Wizards of the Coast / Scryfall

No additional ruling has been published for this card.

Interactions with other cards

These cards' text mentions Eldrazi Horror.

Wharf Infiltrator

Skulk (This creature can't be blocked by creatures with greater power.) Whenever this creature deals combat damage to a player, you may draw a card. If you do, discard a card. Whenever you discard a creature card, you may pay {2}. If you do, create a 3/2 colorless Eldrazi Horror creature token.

Otherworldly Outburst

Target creature gets +1/+0 until end of turn. When that creature dies this turn, create a 3/2 colorless Eldrazi Horror creature token.

Emrakul's Evangel

{T}, Sacrifice this creature and any number of other non-Eldrazi creatures: Create a 3/2 colorless Eldrazi Horror creature token for each creature sacrificed this way.

Shrill Howler // Howling Chorus

Creatures with power less than this creature's power can't block it. {5}{G}: Transform this creature. Creatures with power less than this creature's power can't block it. Whenever this creature deals combat damage to a player, create a 3/2 colorless Eldrazi Horror creature token.

Extricator of Sin // Extricator of Flesh

When this creature enters, you may sacrifice another permanent. If you do, create a 3/2 colorless Eldrazi Horror creature token. Delirium — At the beginning of your upkeep, if there are four or more card types among cards in your graveyard, transform this creature. Eldrazi you control have vigilance. {2}, {T}, Sacrifice a non-Eldrazi creature: Create a 3/2 colorless Eldrazi Horror creature token.

Desperate Sentry

When this creature dies, create a 3/2 colorless Eldrazi Horror creature token. Delirium — This creature gets +3/+0 as long as there are four or more card types among cards in your graveyard.

Enlightened Maniac

When this creature enters, create a 3/2 colorless Eldrazi Horror creature token.

Foul Emissary

When this creature enters, look at the top four cards of your library. You may reveal a creature card from among them and put it into your hand. Put the rest on the bottom of your library in any order. When you sacrifice this creature while casting a spell with emerge, create a 3/2 colorless Eldrazi Horror creature token.