Although in some cases it may make it harder to Synchro Summon, combining this with "Grave of the Super Ancient Organism" will prevent your opponent's Level 6 or higher Special Summoned monsters from attacking or activating their effects while letting your Water/Level 6 Synchro Monsters be able to attack and activate their effects. A perfect example is "Brionac" since it will become a Level 5 monster, evading the effect of "Grave of the Super Ancient Organism". Another good possibility is "Dewloren, Tiger King of the Ice Barrier".
This card can be useful when using an "Atlantean" Deck that focuses less on Extra Deck support. Through the effect, "Atlantean Dragoons" will be able to attack directly with its own effect, while also letting "Atlantean Marksman" get through an opponents monster frontline to deal damage, allowing the easy Summon of "Atlantean Attack Squad". If both "Marksman" and "Dragoons" are on the field, and "A Legendary Ocean" is present, it is likely that you will be able to deal over 6000 damage in a single turn.
This card can be useful in a "Nekroz" Deck, as it reduces the level of the Ritual Monsters in your hand, allowing them to circumvent the Level-specific restrictions many of them have. For example, "Nekroz of Gungnir", a Level 7 Ritual Monster, prevents you from using a Level 7 monster to Summon it, but with this card reducing its level by 1, you can use "Nekroz Kaleidoscope" and send a Level 6 monster from your Extra Deck to cover the Summon with one card (or use a Level 9 monster to Summon "Nekroz of Gungnir" and "Nekroz of Unicore", now a Level 3 monster, simultaneously).