Muldrotha works best with cheap permanents, especially ones that are sacrificed as part of their activation costs: Pernicious Deed becomes a repeatable board wipe, Mystic Remora is downright broken when you never need to pay for its cumulative upkeep, Caustic Caterpillar keeps blowing up stuff, and so on
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The deck is actually really good at getting in chip damage with Masked Meower, Molten Gatekeeper, etc so usually you dont need to deal all 20 with the giant but I think you would be surprised how easy it is to get 20 creatures in the gy with stinkweed imp
Shisato, Whispering Hunter is a scion of Kamigawas lethal Orochi snake-people, and can potentially stun an enemy players mana many turns in a row as long as his blows can reach them
Low-cost Infect creatures lead to players abusing cheap pump cards to score a 10-poison hit as early as turn 2, which's not helped by the fact that two of said low-cost creatures have built-in evasion