Keldeo EX (EX) is the perfect attacker, since it does more damage for each Water Energy attached to it
You can only use each effect of "Catoblepas, Familiar of the Evil Eye" once per turn
For example, if two or more effects attempt to modify how many counters would be put onto a permanent you control, you choose the order to apply those effects, no matter who controls the sources of those effects
On top of that, any battles that take place between your Performapals and your opponents monsters will inflict zero battle damage to you , leaving your Performapals safe and sound and your life points intact
(2) The effect is also not bad because you can pull a trap that can support his Fusion Monster made with his own effect
The trade-off is that secondary market demand for individual shiny cards varies considerably