2021-03-19 : Because a spell with overload doesn't target when its overload cost is paid, it may affect artifacts with hexproof or with protection from red.

2021-03-19 : If you are instructed to cast a spell with overload “without paying its mana cost,” you can't choose to pay its overload cost instead.

2021-03-19 : If you don't pay the overload cost of Vandalblast, that spell will have a single target. If you pay the overload cost, the spell won't have any targets.

2021-03-19 : To determine the total cost of a spell, start with the mana cost or alternative cost you're paying (such as an overload cost), add any cost increases, then apply any cost reductions. The mana value of the spell is determined by only its mana cost, no matter what the total cost to cast that spell was.