Card

Nether Void

Mana cost {3}{B}

Whenever a player casts a spell, counter it unless that player pays {3}.

Part of 1 known combo, one of them two-card. 3 official rulings.

Bracket

B1 Exhibition — Not in the same deck as its two-card combo partner: Guile
B2 Core — Not in the same deck as its two-card combo partner: Guile
B3 Upgraded — allowed: Its two-card combos are not early, which Bracket 3 allows
B4 Optimized — allowed: No restriction beyond the banned list
B5 cEDH — allowed: No restriction beyond the banned list

Bracket: Lotus Vault analysis, with Commander Spellbook flags

1 known combo, one of them two-card.

Guile + Nether Void
Produces: Infinite magecraft triggers, Infinite storm count
View on Commander Spellbook

2009-10-01 · Wizards of the Coast
The ability triggers whenever any player (including you) casts a spell of any type.
2008-10-01 · Wizards of the Coast
This has the supertype world. When a world permanent enters, any world permanents that were already on the battlefield are put into their owners' graveyards. This is a state-based action called the "world rule." The new world permanent stays on the battlefield. If two world permanents enter at the same time, they're both put into their owners' graveyards.
2004-10-04 · Wizards of the Coast
This is not an additional cost, it is a triggered ability.

Rulings: Scryfall · Wizards of the Coast