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
Altar of Dementia by sacrificing
Putrid Goblin.
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.
Resolve the
Altar of Dementia ability, causing target player to mill cards equal to
Putrid Goblin's power.
Repeat.
Results
Infinite +1/+1 counters on a creature.
Infinite death triggers.
Infinite creature ETB.
Infinite creature LTB.
Infinite mill.
Infinite creature sacrifice triggers.
Infinite self-mill.
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.