Since the effect grabs "X or less" you can put extra mana into the X for your trigger and still get what you really want or need from your deck, even if it's cheaper
There are so many fun ways you can use this, but it is also a great resource to have in your classroom for when students have a bit of downtime
With a set reprint on the horizon, it's unclear how the cards value will be affected but being an Umbreon, it will surely hold a lot of value going forward regardless
Origin Forme Dialga VSTAR hits for a minimum of 80 damage with one Metal Energy, but five gives you access to Star Chronos
He's Semi-Limited, so the most you can play is 2
For the rest of this turn after this card resolves, you cannot Special Summon from the Extra Deck, except Pyro monsters