Number M, also known as Malefic Number (Sin Number in the OCG), is a sub-archetype of the "conditions treat them as both their original counterparts' names and as " " monsters." archetype in . Their
Like the "Malefic" archetype, only one copy of them can be on the field, and they are destroyed if no Field Spell Card is in play. Unlike this archetype, however, their restrictions are limited to the controller only controlling 1 "Number M" monster (possibly for the purpose of ). Similarly, "Number CM" monsters prevent their controllers from Summoning their base counterparts. Furthermore, their controllers' other monsters are allowed to attack.
"Number M" and "Number CM" monsters can be Summoned via a way similar to Chaos Xyz Evolution, by using their original counterparts as the Xyz Material. However, they cannot use themselves to be Summoned; for example, to Xyz Summon "Number M101: Silent Honor ARK", you cannot use another "Number M101: Silent Honor ARK" as the Xyz Material, but rather its original counterpart with its original Attribute of WATER.