The most weaknesses a Pokemon can have at once, using only natural dual-typing typings, is seven. This amount is reached by the following types, and the following Pokemon:
- Ice/Grass, the type of Snover, Abomasnow and Mega Abomasnow,
- Grass/Dark, the type of Nuzleaf, Shiftry and Cacturne,
- Grass/Psychic, the type of Celebi, Exeggcute and Exeggutor,
- Figthting/Rock, the type of Terrakion,
- Psychic/Rock, the type of Lunatone and Solrock, and
- Rock/Dark, the type of Tyranitar and Mega Tyranitar.
The first three are the worst of all, as one of each of their weakness is also a quad-weakness. These unfortunate combinations are caused primarily by a lack of overlap in weaknesses and resistances.
We can go better than this, though. If Forest's Curse is used on a Dragon/Ice type Pokemon, it gains weaknesses to Fire, Ice, Poison, Flying and Bug in addition to its five existing weaknesses, bringing its total weaknesses to ten, the highest possible under normal circumstances.