Thought Sponge — ruling 1

Thought Sponge checks how many cards were drawn by opponents this turn, even opponents who have left the game. The greatest number drawn by a single opponent is how many +1/+1 counters it enters with.

Thought Sponge — ruling 2

Thought Sponge checks the total number of cards drawn by each opponent, not how many were drawn due to a single instruction.

Thought Sponge — ruling 3

Use Thought Sponge's power as it last existed on the battlefield to determine how many cards to draw for its last ability. If that number is negative, you neither draw nor discard cards.

Thought Sponge — ruling 4

Thought Sponge gets its +1/+1 counters at the moment it enters the battlefield. There's not a time that it's on the battlefield before its replacement effect has applied.

Thought Sponge : règles, fonctionnement et interactions (MTG)

Thought Sponge is one of those cards players keep asking about. Here is, in plain words, what its official text says, the rulings published by Wizards of the Coast, and the combos players actually run.

Official card text

Flash This creature enters with a number of +1/+1 counters on it equal to the greatest number of cards an opponent has drawn this turn. When this creature dies, draw cards equal to its power.

How it works : Thought Sponge

Original English text — Wizards of the Coast / Scryfall

#1August 23, 2019· Wizards of the Coast
Thought Sponge checks how many cards were drawn by opponents this turn, even opponents who have left the game. The greatest number drawn by a single opponent is how many +1/+1 counters it enters with.
No other card is named in this ruling.
#2August 23, 2019· Wizards of the Coast
Thought Sponge checks the total number of cards drawn by each opponent, not how many were drawn due to a single instruction.
No other card is named in this ruling.
#3August 23, 2019· Wizards of the Coast
Use Thought Sponge's power as it last existed on the battlefield to determine how many cards to draw for its last ability. If that number is negative, you neither draw nor discard cards.
No other card is named in this ruling.
#4August 23, 2019· Wizards of the Coast
Thought Sponge gets its +1/+1 counters at the moment it enters the battlefield. There's not a time that it's on the battlefield before its replacement effect has applied.
No other card is named in this ruling.