Relics take 300x Pluton
Mythic take 300x Chunk of Beitetsu
Empyreans take 300x Riftborn Boulder
I killed several delve NMs so far
Tax'et, Kurma, Mata, Raptor, all droped 1 item. Got lucky on Supernal Chapuli he dropped a case which had 3. This is going to be one long grind. Since its loot pooled it may be worse then plates.
What I got out of it is that delve NMs drop 1 item or a rare chance to drop a case which has multiple. We will have to see what new BCNMs drop since nobody has seals yet.