Sharpedo / Victini could be good because of T2 discard as well as slowking to manipulate their first 3 cards of their deck. That could potentially lock magneboar before its started. Only other suggestion for such a deck would be a secondary pokemon that can do damage such as sneasel and beat up
Flip a coin for every pokemon in play. This attack does 20 damage times the number of heads.
Thats the possibility of 240 damage and you can reflip due to victini's power to try to knock out their active. I could see this as a very flippy donk deck
roserade could be added to the sharpedo /victini combo to counter magnezone to an extent since it can't use its poke power if it has a special condition