It's been done before, and all you have to do is name the ability something that isn't too far off from the mechanic and shove that name in there without explanation in the card text (but in the notes).
Example:
Text: When summoned, set all enemy creatures' ATKs to 0 for 1 turn. Legendary.
Notes: Legendary - While a copy of this card is on your side of the field, you cannot generate or play a new copy onto the field.