Vale Tudo (misspelled as "Val Tudo" in Deception) is a fighting style used by Nightwolf in Deception and Armageddon and by Siro in Mortal Kombat: Conquest. Vale Tudo is Portuguese for everything is permitted or, in looser terms, anything goes. It is described as a Combat Sport having little or no rules/limitations in unarmed combat.
Val Tudo is a bare fisted fighting style that has very few rules. It is a precursor to modern day MMA, and sometimes the terms are used interchangeably.