The eighteenth card is One for One, a card that lets you discard a monster to special summon a level one monster from your deck or hand. There are various cards that this can combo well with, the Black and White Stones of Legend, for example, in fact a number of archetypes have level one support that need to be on the field for a time. There are also cards like Copycat and Flamvell Guard that can be summoned with this and can have a good amount of attack and defense. You can also use this card to help set up for things like Law of the Normal and Triangle Power. It is a summon that can search the deck for you, and can be useful in some of the archetypes and level one monsters have some support of their own as well so a pretty good card.