Pikachu, the Electric-Type Mouse Pokemon has the abilities Static and Lightning Rod. Static would be pretty useless against Thor, seeing that if Thor hits Pikachu with one swing of Mjolnir, Pikachu is instantly dead due to the frail defenses (even with the Light Ball or Eviolite) of the mouse. With Lightning Rod, all electricity will get absorbed by Pikachu and raise its Special Attack. This would make Thor’s main arsenal of offense useless, but the guy is smart. He’ll stop attacking Pikachu with lightning.
There are many attacks Pikachu can use (assuming we are using all attacks it can learn from all generations, from past-evolutions, and able to use all Z-Crystals, including Pikashunium Z), but I don’t think any of them will do anything to Thor. Even the Z-Crystals would do nothing to Thor, since he’s capable of trading blows with Thanos and took radiation and solar damage from a star, and he can redirect electrical attacks aimed at him (for the most part) to somewhere else.