If you cast Chemister’s Trick with overload, only creatures you don’t control that are on the battlefield when Chemister’s Trick resolves are affected. Creatures that come under another player’s control later in the turn are not.

The controller of a creature that attacks if able still chooses which player or planeswalker it attacks.

If, during a player’s declare attacker’s step, a creature is tapped, is affected by a spell or ability that says it can’t attack, or hasn’t been under that player’s control continuously since the turn began (and doesn’t have haste), then it doesn’t attack. If there’s a cost associated with having a creature attack, the player isn’t forced to pay that cost, so it doesn’t have to attack in that case either.

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.

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.

Note that if the spell with overload is dealing damage, protection from that spell’s color will still prevent that damage.

Overload doesn’t change when you can cast the spell.

Casting a spell with overload doesn’t change that spell’s mana cost. You just pay the overload cost instead.

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.

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.