Activate Goblin Bombardment by sacrificing another nontoken non-Human creature
When the creature dies, its undying ability triggers, returning the creature from your graveyard to the battlefield with a +1/+1 counter on it.
Activate Goblin Bombardment by sacrificing the creature with a +1/+1 counter on it.
When the creature dies, its persist ability triggers, returning it from your graveyard to the battlefield with a -1/-1 counter on it.
Resolve the Goblin Bombardment abilities from step 1 and 3.
Repeat.
This loop sets up an eternal cycle of rebirth and sacrifice by turning Mikaeus, the Unhallowed and Isilu, Carrier of Twilight into a mutual admiration society for your non-Human creatures, granting them both undying and persist simultaneously. When you feed a creature to Goblin Bombardment, undying brings it back with a +1/+1 counter, which then neutralizes the -1/-1 counter from persist when it dies again, allowing the two abilities to endlessly catch the creature in a loop of resurrection. Because Eirdu, Carrier of Dawn eases your mana requirements by giving your creature spells convoke before you transform her into Isilu, you can easily rebuild your board while Goblin Bombardment turns every iteration into an infinite stream of damage.