Gyarados, but with SCARY early pressure, courtesy of Crabominable's building damage. This cheap attack arguably make the crab just a better Exeggutor. Heal with Irida, clear status with PCL, tank with Capes.

Speaking of Cape, Karp can Leap Out of the way when going second, but it's severely exposed if forced to lead going first. This is why I include a single Fishing Net, to get back a dead Magikarp on the off-chance your Poke Balls just can't hit any. You could say X Speed or Leaf are just better answers, but those don't cover the rogue Hitmonlee Stretch Kick when you just can't find a Cape early enough.

Theoretically, it even pairs well with Crabrawler being untargetable by Net, but sadly, I think the synergy remains just in the realm of theory. If you're in a position of having both a Crab and a Karp KOed, it's most likely too late to start building a Gyarados, since not even Crabominable's fat HP can tank for that long if you're 2 points down.

Regardless! Net is not the reason this deck is good. Hit them hard with Crab, then hit them again. If they still don't die, then it's late enough for Gyarados to rage through whatever's left!