Aerodactyl EX

While Aerodactyl is a pretty capable Pokemon unto itself, its ability to halt Evolution for the opponent's active Pokemon from the bench is pretty huge. Arbok can take perfect advantage of this, helplessly trapping unevolved Pokemon in the active spot and clearing them out with ease. Sabrina can help by forcing a switch, and can potentially ensure that the chain never stops.

Kangaskhan is here to act as an early-game wall with potentially good damage output, and Marshadow has the advantage of being able to just sit on the bench, waiting for its chance to come in and absolutely slam whatever KOed a teammate for heavy damage.

Running two energy types can be a bit of a pain, but everything in this deck (save Ekans) runs with 1-2 energy, one of which is always colorless, so it generally shouldn't be too problematic.