Edison format ruling
Cost Down

Card effect (current official text)Discard 1 card; for the rest of this turn, reduce the Levels of all monsters in your hand by 2 (even after they are Summoned).
Rulings
- The Level of a monster which is Summoned using Cost Down is still decreased by 2 after Summoning. The 2 Level reduction lasts until the End Phase.
- When you Ritual Summon while Cost Down is active, the Level Stars that you need is not changed, even if you are using Contract with the Abyss or Earth Chant.
- You can use multiple Cost Downs in the same turn and their effects accumulate, so 3 Cost Downs lowers the level by 6 Stars.
- While A Legendary Ocean and 1 Cost Down are active, your WATER monsters are reduced by 3 Stars.
Rulings data courtesy of Format Library — formatlibrary.com. Spotted an inaccuracy? Flag it in the Edison forum — sourced change requests get reviewed.