As for what could be in the missing spots, 439 is missing, which is a white card between Dion and Minwu, 457 is likely a red card before Clive alphabetically, a multicolour card at 485 between The Emperor of Palamecia and Garland, 504 between Rufus and Sephiroth, and 515 between Vivi and Xande
A combination of power in the game, rarity and popularity as a Pokemon are what has driven the price of Rayquaza GX rainbow rare
Yenna, Redtooth Regent Yenna, Redtooth Regent can generate a lot of constellation triggers for things like Archon of Sun's Grace and can ramp pretty nicely with cards like Wild Growth, but is that better than running a more efficient Selesnya commander with a card draw ability
Tribal is a card type, but its other types dictate whether its a permanent
From February 10March 2, a new iteration of Arena Powered Cube will beckon you to the battlefield with the lure of a supercharged deck