When Dualcaster Mage enters the battlefield, it triggers, copying Thunderous Debut.
Activate Goblin Bombardment by sacrificing Dualcaster Mage.
When Dualcaster Mage dies, Mortuary triggers, putting Dualcaster Mage on top of your library from your graveyard.
Resolve the Goblin Bombardment ability, dealing 1 damage to any target.
Resolve the copy of Thunderous Debut, causing you to look at the top twenty cards of your library and put Dualcaster Mage and up to one other creature card onto the battlefield.
Repeat from step 3.
Results
Infinite damage.
Infinite death triggers.
Infinite ETB.
Infinite LTB.
Infinite magecraft triggers.
Infinite sacrifice triggers.
Put all creature cards from your library onto the battlefield.