You must control this face-up card to activate and to resolve this effect
This, in turn, would reduce the number of players accumulating excessive amounts of energy, with some currently reaching double digits
Another reason that makes understanding this card more complicated is that the floor on it is very low - your opponent can anticipate it and kill your only creature or your strongest creature in response
Given its in-game usefulness and strength, along with its amazing card art, its no wonder we see Greninja ex at the top of the most valuable Twilight Masquerade cards list
However, her ability certainly makes her stand out
Iron Cage X SPELL Continuous When this card is activated: Send 1 monster you control to the GY, or if "Golden Castle of Stromberg" is in a Field Zone, you can send 1 monster your opponent controls to the GY, instead