Is Murktide Regent legal in Standard, Modern, and Commander?

Murktide Regent is legal in: Modern, Legacy, Vintage, Commander.

Murktide Regent

Q: What type of card is Murktide Regent?

Murktide Regent is a Creature — Dragon. Its oracle text reads: "Delve (Each card you exile from your graveyard while casting this spell pays for {1}.) Flying This creature enters with a +1/+1 counter on it for each instant and sorcery card exiled with it. Whenever an instant or sorcery card leaves your graveyard, put a +1/+1 counter on this creature."