Cast the Dinosaur in your hand by paying its mana cost. It will enter with a coin counter due to Blue.
Activate Goblin Bombardment by sacrificing the Dinosaur.
When the Dinosaur dies, Athreos's second ability triggers, returning the Dinosaur from your graveyard to the battlefield. It will enter with a coin counter due to Blue.
Resolve the Goblin Bombardment ability.
Repeat from step 2.
By placing a coin counter on Blue, Loyal Raptor via Athreos, Shroud-Veiled's end step trigger, you set up a marvelous replication engine for any subsequent Dinosaur you bring to the battlefield. Because Blue endows your incoming Dinosaurs with a matching copy of every counter it bears, each new reptilian arrival enters with its own coin counter pre-attached. This ensures that when you feed the creature to Goblin Bombardment to ping away at your opponents, Athreos immediately resurrects it from the graveyard straight back to your side of the battlefield, fully prepared to repeat the cycle indefinitely.