For tutor targets, one of the best is Unesh, Criosphinx Sovereign, which is sort of a hidden commander for the deck, supercharging all our sphinxes like Defiler of Dreams
Even though its ability works completely in context with the rules of MTG, it was likely made an acorn card so you could only partner it with other Unfinity commanders
Source: Magic: The Gathering/YouTube Magic: The Gathering Arena Released September 27, 2018 ESRB T for Teen // Blood and Gore, Mild Fantasy Violence Developer(s) Wizards of the Coast, Wizards Digital Games Studios Publisher(s) Wizards of the Coast Engine Unity Multiplayer Online Multiplayer Franchise Magic: The Gathering Platform(s) PC, Android, iOS Genre(s) Digital Card Game OpenCritic Rating Strong
And, you might be surprised to learn that the most common way a Defender deck wins is through combat damage
15 Safari Zone HD Remaster Common based on Vending Series 3 card Voltorb LV
Rebound is great for spells matter decks, and Faithless Salvaging is probably better than the next card if your goal is to stock the graveyard with specific targets
