At the beginning of your combat phase, Duke Ulder Ravengard triggers, giving Mondrak haste and myriad until end of turn.
Declare Mondrak as an attacker.
Mondrak's myriad ability triggers, creating two token copies of Mondrak that are tapped and attacking each opponent.
Put all Mondrak tokens into your graveyard due to the legend rule.
When the Mondrak tokens die, Ratadrabik of Urborg triggers that many times.
Resolve the first trigger, creating a number of nonlegendary token copies of Mondrak equal to 2^(the number of Mondraks you control) that are 2/2 Zombies.