Putrid Goblin does not have a -1/-1 counter on it.
You have had at least one Zombie enter the battlefield under your control this turn.
Steps
Activate
Thermopod's second ability by sacrificing
Putrid Goblin, adding ({R} magic symbol) .
When
Putrid Goblin dies, its persist ability triggers, returning it from your graveyard to the battlefield with a -1/-1 counter on it.
When
Putrid Goblin enters the battlefield,
Geralf's second ability triggers, putting a number of +1/+1 counters on it equal to the number of other Zombies that entered the battlefield under your cotnrol this turn.
Repeat.
Results
Infinite +1/+1 counters on a creature.
Infinite creature ETB.
Infinite creature LTB.
Infinite death triggers.
Infinite red mana.
Infinite creature sacrifice triggers.
Metadata
Bracket tag
ExhibitionBracket 1+
For any deck
1
2
3
4
5
1 · Exhibition5 · cEDH
Bracket tags are estimated from the cards and results of each combo, as a guideline rather than a strict classification.