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Selfless Savior, Skrelv, Defector Mite, and Mother of Runes are examples of mana-free protection that we can cast before casting our commander (protection from color can also double as evasion!), and we also have cards like Brass Squire which can equip protection for free

Moonshaker Cavalry is solid if you can get the mana, but usually you want to be dropping Akromas Will when you have six or seven mana, not eight, with some leftover to play another creature or a removal spell

Do they synergize with the other thallids spore counters

Obviously, one could remove the Hexproof counter on Leatherhead to blast the nearest Rhystic Study to smithereens