Mzed, Mercenary Leader 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

Mono Eminence — If Mzed is on the battlefield or in your command zone and your deck's color identity is mono-red, creatures you control have haste. At the beginning of your combat step, create a 1/1 red Mercenary creature token with "This creature can't block." Partner (You can have two commanders if both have partner.)