Its a good fit in lifegain/life drain decks, zombie typal decks, or even Bloomburrow -inspired bat decks that care about gaining and losing life
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to get you up to speed, heres a video from WotCs own Gavin Verhey explaining how it works
Its practically equal to a -1/-1 counter, the effect is the same, and I think designers didnt want a creature to have negative power
Bloodroot Apothecary is a solid companion to infect that locks out some token sacrificing strategies
This means its generally reserved for Paper Vintage, which is an expensive proposition, to say the least