Niadra of the Numberless

For each {u} or {b} in the mana costs of spells you cast, you may sacrifice another Rat creature rather than pay that mana.
{2}{u}{b}, {t}: Put X 1/1 black Rat creature token onto the battlefield, where X is the greatest converted mana cost among spells cast this turn.
An army without number. A brilliance without mercy.
A power without limit.