RedUndead40 says
This set is only the beginning of the offerings that will come to Owl Central Games, including Starter Decks and more!
But as with Articuno ex, you can use Misty or the Mythical Island Vaporeon to stack a Gyarados ex with energy
For example, exiling a Battle Brawler (a creature with As long as you control a red or white permanent, Battle Brawler gets +1/+0 and has first strike) with Soulflayers delve ability wont cause Soulflayer to have first strike, even if you control a red or white permanent
This seasons Standard decks probably arent the best indicators of required counts as the mana is so absurdly good, but looking back in time, you probably want 9-11 sources for a splash of a couple key effects and fifteen+ for a solid commitment
My opponent, GaJol, was down to two life