With Weezing not even needing to attack to counter meta picks, players can safely play it with Giratina Ex as well, as its ability can only be used in place of attacks with the advantage of getting free Energy
The player might not need to play the Eevee V to summon the Eeveelutions to the field, but it's worth using on its own, as its one energy Collect attack lets the player draw three cards, while its three energy Brave Buddies attack deals 160 damage, if a Supporter card has been played during the player's turn
The most expensive Pokmon Mega Evolution card is Mega Charizard EX (Full Art / Secret Rare) , as it combines Charizards iconic status, limited print runs, and consistently high collector demand, often placing it at the top of Mega Evolution secret rare price guide
As for eternal formats, the legality will depend on each card individually
Auras have always been a problem, as they allow the opportunity for card disadvantage (since the opponent's kill spell will essentially destroy the creature and the aura on it), so R&D has spent a lot of time trying to come up with different ways to offset that card disadvantage
You can hold up just two mana and laugh at any board wipe that comes your way