2021-06-18 : Because a spell with overload doesn't target when its overload cost is paid, it may affect permanents with hexproof or with protection from the appropriate color.

2021-06-18 : Casting a spell with overload doesn't change that spell's mana cost or mana value. You just pay the overload cost instead.

2021-06-18 : Effects that cause you to pay more or less for a spell will cause you to pay that much more or less while casting it for its overload cost, too.

2021-06-18 : 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.

2021-06-18 : If you don't pay the overload cost of a spell, that spell will have a single target. If you pay the overload cost, the spell won't have any targets.

2021-06-18 : Overload doesn't change when you can cast the spell.