There is several variants of Highlander rules (mainly ban lists) but most of them have the following rules
You can only have 1 card of each type except for basic lands.
Your deck must have at least 100 cards in it.
Highlander
Published
There is several variants of Highlander rules (mainly ban lists) but most of them have the following rules
You can only have 1 card of each type except for basic lands.
Your deck must have at least 100 cards in it.
MTG blog 