If Raving Dead can't attack the chosen player for one of the above reasons but it can still attack elsewhere, you may choose to have it attack another player, attack a planeswalker, or not attack at all.

If your turn has multiple combat phases, Raving Dead's ability triggers at the beginning of each of them. Ignore any choices made during previous combat phases that turn.

The last ability triggers and resolves after combat damage has been dealt. For example, if an opponent has 17 life and Raving Dead deals 2 combat damage to them, they will end up at 8 life.

If, as attackers are declared, Raving Dead is tapped, is affected by a spell or ability that says it can't attack, or hasn't been under your control continuously since your turn began (and doesn't have haste), then it doesn't attack. If there's a cost associated with having Raving Dead attack the chosen player, you aren't forced to pay that cost, so it doesn't have to attack that player in that case either.

Raving Dead must attack the chosen player if able, not a planeswalker controlled by that player.