For Pixelmon Reforged 9.0.0+
You'll need both the Datapack and Resource Pack for it to work properly!
This is a Datapack and Resource Pack that adds an Ice/Poison variant to Beedrill, including a Mega Evolution and signature move. You can obtain this form by evolving Kakuna while in a snowy biome.
Included is a Mega Evolution, which can be used by having Icicle Beedrill hold an Ice Memory (because custom megas are bugged with mega stones right now).
Icicle Beedrill's signature move is Icicle Injection, a 100 base power Ice move that has a guaranteed chance to poison.
Hopefully this will be a good example for others looking to make their own datapacks!