Enchantment, 2UU (4) Whenever a player plays a spell that counters a spell that has been played or a player plays a spell that comes into play with counters, that player may counter the next spell played or put an additional counter on a permanent that has already been played, but not countered.1
Illus. Stephen Daniele
In simpler text, this card means "Whenever a player plays a counterspell or plays a card that makes use of counters, you get to choose to do one of the following: counter the next spell; or put a counter on a card that has counters." [Unhinged FAQ 2004/11/15]
If you choose to put a counter on, find a permanent in play with at least one counter on it and put an additional counter of the same kind on it. If it has more than one kind of counter on it, you can choose which kind to add. [Unhinged FAQ 2004/11/15]
All tournament formats have banned cards from Unhinged.
Unhinged
(Rare)