As for returning cards, Managorger Hydra grows huge incredibly quickly in this deck, and Semester's End can protect you from a board wipe, while also dishing out counters
Case of the Locked Hothouse If ever there was a card that looked like someone just straight up designed it for Cube, Case of the Locked Hothouse is it
There is also the ever-helpful Illumineers Trove, and two starter decks
For the deck's strategy, I wanted to capture the core gameplay loop of FINAL FANTASY XIV
But they are here in my Honorable Mentions since as planeswalkers, they're the most answerable permanent by attacking, removal or burn
(Whenever this becomes the target of a spell or ability an opponent controls, counter it unless that player discards a card.) Whenever another nontoken Vampire you control dies, you may pay and exile it