Éomer cannot be blocked and killed by an opponent.
You have at least three opponents.
Steps
Declare Éomer as an attacker.
Éomer's myriad ability triggers, creating at least two token copies of it tapped and attacking each other opponent.
Put all Éomer tokens into your graveyard due to the legend rule.
When the Éomer token(s) die, each Éomer token triggers, untapping all creatures you control and causing you to get an additional combat phase after this one.