Poison
Fire
Ice/Steel
Poison is such an underutilized type in the first place, while the STAB is possibly the most trolled STAB in the game [How are you not Super-effective on Bug? Or even Water?!], you have to admit more or less the only Poison types with competitive stats nowadays is Crobat, Roserade and Arceus Poison.
This is an excellent time to test the effectiveness of the Poison type outside of being something that sets up Toxic Spikes, or just exists to troll. Nidoking manages fine without using Poison STAB, so if he can do it, surely CAP3 can too!