Unfortunately, Koraidon rarely receives meta-relevant cards, but Miraidon has been featured in multiple different strategies and a few of its versions are incredibly powerful
Mega Evolution cards expanded into the Sun & Moon era, where dozens of valuable cards from sets like Team Up and Unified Minds appeared with two Pokemon, at least one of which was Mega Evolved
As long as theyre milling more than 40 permanents (which is rather likely), they should die on the spot
Veteran Explorer needs to die for this to happen, whereas Avatar of Growth simply needs to enter play, and it often does so for just 3 mana
Of course, the white border was a lot more obvious than a simple line of text, and it had notable effects on the aesthetics of the cards that used it