When it comes into play, you pick a color, letting you tap it to generate four mana of that color
In MTG, Companion is a keyword that allows you to put a specific card from outside the game into your hand, for three mana, as long as you build your deck to fit particular requirements
If the Pokmon this card is attached to is Knocked Out by damage from an attack from your opponents Pokmon, draw cards until you have 7 cards in your hand.
The easiest yes would be if youre adding a splash plus extra late game cards on the play, in which case an extra land might suit your new curve better than whatever you had
You can still play items, attach energy, and play tactically, but the moment you play down your Mega Evolution, it becomes your opponent's turn
However, I would have thought the protagonist from one of the series best games would be a prime candidate for some tight theming