Caterpie+Arbok. It's a Bug/Poison type, and is more or less a giant caterpillar that never metamorphosed.

Doduo+Bulbasaur. Grass/Flying. It looks like a combination of a kiwi, a corgi, and a bulb of garlic.

Golem+Paras. Bug/Ground. It has little olive trees growing on its back and lives in arid regions.

Magneton+Poliwhirl. Steel. It's using Encore here, and looks pretty Disney...

Rapidash+Seadra. Fire/Water. It looks more like a dragon than a horse combined with a seahorse.

Oddish+Slowpoke. Water/Grass. It lives in mossy caves and is not very bright. Can't stand sunlight.