This... would... be... amazing...
The catch is putting a value on the summon. For example using it for Utopia gives you 4 uses of the effect versus 2 normally; whereas using it on Baby Tiragon only gives you 1 use instead of the normal 3.
I just built an Evolsaur deck and this would be great for Laggia. Its like getting double use out of Solemn Judgment.
Evolsaur Laggia
2 Level 4 Dinosaur-Type monsters
During either player's turn, when a monster(s) would be Normal or Special Summoned, OR a Spell/Trap Card is activated: You can detach 2 Xyz Materials from this card; negate the Summon or activation, and if you do, destroy that card.