Black Knight is great against Blue/White Control, Mono White, and any other deck that relies on Swords to Plowshares, Wrath of God, and Balance for creature removal (under Alpha rules, protection from white makes Black Knight immune to Wrath of God and Balance)
Sin, Unending* Sin comes in and takes away the sin of playing with all those counters, and magnifies them onto its flying, trampling self
Thassa also works great with cards that have enter the battlefield triggers or might have other effects on them that might be preventing you from attacking or activating abilities
While a 1/1 might not be much to write home about, as soon as you get ten permanents in play and you get the City's Blessing, all your Saproling creatures get +2/+2 and suddenly become 3/3 threats
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