Dimensional monsters are monsters that have the clause "During the End Phase of the turn this monster was Summoned: Banish it." Dimensional monsters can be Normal Summoned while banished by activating specific effects of theirs. So far, the only confirmed way of Normal Summoning them while banished is by adding an X (X being the same level as the Dimensional monster) level monster from the field to the top of the Deck, and that monster is returned face-up instead of face-down. It is unknown if there will be other ways to Normal Summon Dimensional monsters while banished. Dimensional monsters also have this clause after being Normal Summoned by their effects: "This card cannot be banished if Summoned by this effect."