The Altar is a confusing part of the game. Don't rush it, take the time to read this piece as it will help you understand how the Altar works and how it can help you.
The Altar (Version 1), unlocked at Stage 400 in the World Map serves one main purpose:
- The Altar is the place where you can sacrifice a select few of your heroes to get alternate (better) versions of your heroes. This includes sacrificing Sicri or Kalethah to get Nushkilan. Once placed into the Altar, the heroes will return after you use Dark Ritual. Any hero who can be swapped out for another hero has a chance to come back as the better version. It is not a guarantee. If you place more than 3 heroes in the Altar to be sacrificed, you will only get back 3 after the Dark Ritual. The next time you use Dark Ritual, more will return. Any time you put a hero into the Altar who will be sacrificed (There are no numbers underneath it), there is a chance the hero will not return. If this happens, wait until your next Dark Ritual, they should return then.
- While you can put heroes in to receive shard packs in return, it is generally not advised at Stage 400. Wait until you have unlocked the second version of the Altar at Stage 1500. Any heroes placed into the Altar can give back more hero shards, depending on the hero you sacrifice, including their current gear (gold stars on their portrait) and rarity.
Several heroes (see below) can reincarnate as more powerful versions, often buffing all hero damage. They won't always return as the improved version; it may require several attempts. Powerful versions may likewise return as their original versions, so don't carelessly put a hero in as you may lose that version of them.
Up to four heroes may be placed on the altar at one time. The altar will show how many shard packs you would get for the heroes currently on it. Up to three basic and/or improved heroes will return for each Dark Ritual.
Gear will cause the altar to produce shard packs or increase their number. Every 10(aka rank or grade) on a hero also yields one shard pack.