While a monster that mentions "Atlantis, City of the Sea Dragon" is on the field, the Levels of all monsters in both players' hands and on the field are reduced by 1. When you Link Summon a "Daedalus" Link Monster, you can reduce the total number of materials by 1 (from Link Rating and from mentioned materials). If this card is in your GY and you control "Umi": You can place this card face-up on your field. You can only use this effect of "Atlantis, City of the Sea Dragon" once per turn.