The Standard Format Changes, sometimes twice a year depending on set releases, will have the most up-to-date rules for tournament play
The three Legendaries combine for 280HP, and the cards Ultimate Ray attack does 150 damage and lets you shuffle your deck for up to three basic Energy cards to attach to your Pokmon in any way you want
But your Summon: Bahamut happens to be an enchantment creature, and dies to Boseiju
Doom Whisperer (Guilds of Ravnica): Not ideal if you think eight is already too many limbs
Other good three-color options include the evergreen Muldrotha, the Gravetide, and Saruman of Many Colors who gets a bit of extra value from having guaranteed access to a high-cost spell in the companion zone
You must follow all normal timing rules for spells cast and lands played using the third ability and must pay all costs for spells cast this way