Right now the description for the Diabolic Altar looks like this:

"Feeding 15 Shards to the Altar will satisfy its hunger.. for now. In return for your submissiveness, the altar will randomly grant you a "Possession" or an "Invocation". For 10 Shards, the Altar will grant you a "Brimstone Core", "Brimstone Imprints" or "Burning Embers", depending on your choice. For 3 shards, the Altar will grant you a "Brimstone Mane"."

However, this is outdated. You can choose which mane shape app you can get from a given amount of Shards, instead of it being random, and it excludes the most recent Altar rewards such as the eye apps. The new description should look like this:

"Feeding 15 Shards to the Altar will satisfy its hunger... for now. In return for your submissiveness, the altar will grant you a "Possession" or an "Invocation" of your choice. For 10 Shards, the Altar will grant you a base or marking applicator, depending on your choice. For 4 Shards, the Altar will grant you a "Demon Eyes" or "Vile Eyes" of your choice. For 3 shards, the Altar will grant you a "Brimstone Mane" or "Shard Fur", depending on your choice."