Putrid Goblin does not have a -1/-1 counter on it.
Mana Needed
({1} magic symbol) ({R} magic symbol) available.
Steps
Cast
First Day of Class by paying ({1} magic symbol) ({R} magic symbol) , causing all creatures that enter the battlefield under your control this turn to get an additional +1/+1 counter put on it.
Activate
Goblin Bombardment by sacrificing
Putrid Goblin.
Putrid Goblin's persist ability triggers, returning itself from your graveyard to the battlefield with a -1/-1 counter on it.
Putrid Goblin enters the battlefield, triggering
First Day of Class, putting a +1/+1 counter on
Putrid Goblin.
Resolve the
Goblin Bombardment ability from step 2, dealing 1 damage to any target.