Corporeal Projection

You choose whether each token is attacking the player or a planeswalker they control as the token is created.

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.

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

Although the tokens enter the battlefield attacking, they were never declared as attackers. Abilities that trigger whenever a creature attacks won't trigger, including the myriad ability of the tokens. If there are any costs to have a creature attack, those costs won't apply to the tokens.

Each token copies exactly what was printed on the original creature and nothing else. It doesn't copy whether that creature is tapped or untapped, whether it has any counters on it or Auras and Equipment attached to it, or any non-copy effects that have changed its power, toughness, types, color, and so on.

If myriad creates more than one token for any given player (due to an effect such as the one Doubling Season creates), you may choose separately for each token whether it's attacking the player or a planeswalker they control.

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.

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

Any enters-the-battlefield abilities of the copied creature will trigger when the token enters the battlefield. Any "as [this permanent] enters the battlefield" or "[this permanent] enters the battlefield with" abilities of the copied creature will also work.

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.

The term "defending player" in the myriad rules (or any other ability of an attacking creature) refers to the player the creature with myriad was attacking at the time it became an attacking creature this combat, the controller of the planeswalker the creature was attacking at the time it became an attacking creature this combat, or the protector of the battle this creature was attacking at the time it became an attacking creature this combat.