Eumidian Wastewaker

If one of the tokens somehow is under another player’s control as the delayed triggered ability resolves, you can’t sacrifice that token. It remains on the battlefield indefinitely, even if you regain control of it later.

Each token must attack the appropriate player if able.

When Eumidian Wastewaker’s first ability resolves, you choose to discard a card or sacrifice a permanent, and then defending player chooses to discard a card or sacrifice a permanent. If one of those players can’t discard a card (such as by having no cards in hand), that player must sacrifice a permanent.

Encore is an activated ability that functions from the graveyard. “Encore [cost]” means “[Cost], Exile this card from your graveyard: For each opponent, create a token that’s a copy of this card that attacks that opponent this turn if able. The tokens gain haste. Sacrifice them at the beginning of the next end step. Activate only as a sorcery.”

If one of the tokens can’t attack for any reason (such as being tapped), then it doesn’t attack. If there’s a cost associated with having it attack, you aren’t forced to pay that cost, so it doesn’t have to attack in that case either.

The tokens copy only what’s on the original card. Effects that modified that creature when it was previously on the battlefield won’t be copied.

If an effect stops a token from attacking a specific player, that token can attack any player, planeswalker, or battle, or not attack at all. If the effect stops the token from attacking a specific player unless a cost is paid, you don’t have to pay that cost unless you want to attack that player.