I see three main ways to beat the Deathmist Raptor
Four Smallpox In an ideal world both you and your opponent would mulligan down to about two cards each and youd win with a Swamp and The Rack
It's very strong in leading a deck, and I like it in a poison deck since it already has toxic for two, you only need hit twice with flying each player to cast their library cards
Combine that with fast mana from Eternal formats and you can get initiative on turn 1
Familiars - A cycle of creatures that reduced the cost of allied-colored spells you play
Hilariously, our best finisher is actually a one-mana 1/1 in Valley Mightcaller, which is basically Champion of the Parish but for Frogs, and it also gets trample, which is a huge, huge upgrade