how to make it like when mob hits me theres a chance of striking it with lighting? a

yes easy there should be a trigger in the procedure called when entity gets hit, add a if block to check if the target that got hit is the player, playerMP if its multiplayer mod, them make another if block nested in it, and have a random chance it strike lightning on the source entity.

hope I could help but I don't know if you understand what I am even saying