When Eternal Skylord enters, amass Zombies 2. (Put two +1/+1 counters on an Army you control. It's also a Zombie. If you don't control an Army, create a 0/0 black Zombie Army creature token first.)Zombie tokens you control have flying.
When Trostani's Summoner enters, create a 2/2 white Knight creature token with vigilance, a 3/3 green Centaur creature token, and a 4/4 green Rhino creature token with trample.
Exchange control of two target creatures you don't control.Flashback . This spell costs less to cast this way, where X is the greatest mana value of a commander you own on the battlefield or in the command zone. (You may cast this card from your graveyard for its flashback cost. Then exile it.)