You can often deploy yourself to follow up, play Filey to deal burn damage, or play Waterry to draw
Sure, its an investment to transform the Eye, but remember it can pay for itself, so its effectively 5 mana to craft, and the back side should more than refund itself with the very first spell you cast for free
If you gain control of a creature "until end of turn," you'll control it during your end step
The fact that it costs only Colorless energy is a plus though, since it allows Ultra Necrozma ex to be put in any deck and still attack without waiting for the correct energy
During either player's turn, when a Spell Card is activated that targets exactly 1 monster you control (and no other cards): You can negate the activation
Newer titles have moved away from the paradigm of the heroes of light collecting the scattered crystals in favor of broader, more convoluted plot-lines, but most games in the series still have a crystalline element somewhere