Yeah, I've beaten that style deck various times with different decks...I'd say I'm 50/50 against it with my tourney Serena deck (not the one I've been playing lately).
I don't really play as Loest at all...just imagined the burn would do the trick combined with free draw from MS and removal with Loest's ability. - There's a reason that it is extremely rare for millstalker decks to go above 300 (although I've seen it done-specifically with the solo-style variant).
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