Delve first appeared in Future Sight on three cards: Tombstalker, Logic Knot, and Death Rattle
I think the best places for a planeswalker are in midrange and control decks, since their main strength lies in gaining incremental advantages over the course of a game
There is plenty of life gain not on this list that still gets some niche cube play as lifegain cards and also plenty of regular cube cube cards that get play but not really as any sort of life gain thing
Its a pattern weve seen countless times with cards like Bonecrusher Giant
Some of these can still be played in your MTG Arena decks, though several have also done time on an MTG banlist or two
The Scorpion God is powerful, viable, and fun, but the most common question I see is whether it or Hapatra, Vizier of Poisons is the better commander