Mordekaiser One For All

so i was playing this one for all match with and my fps dropped like crazy, with only one morde i dont notice, but with more it's terrible. my friend had it too. Where I normally have ~100fps and he around 40, i had around 20-30 fps and sometimes 10, and he had 15 fps and sometimes 5. what causes this and can you fix it.

rito plis fix