Weather abuser (Rain)
Suggested ability: adaptability
Suggested ability: Life orb
Thunder-Perfect accuracy in rain.
hyper beam/Tri Attack-STAB; hyper beam normally isn't a good combination competitively, but when you think about Porygon-Z's High special attack, the boost from the life orb, STAB, and his ability, and it can do dangerous amounts of damage. Tri-attack is still there if you want reliability.
Hidden power[water]/[grass]-Deal with bulky waters like Swampert and Quagsire, or get the rain boost of hidden power.
Ice beam-Covers dragon types or bulky water types like Swampert and quagsire.