According to the official article, their rarity distribution is: 68.3% chance of an uncommon FCA card, 25.7% chance of a rare, and 6% chance of a mythic rare
While the fully upgraded list probably isn't ultra-competitive, it should be pretty decent, based mostly on the power of Kadena, Slinking Sorcerer as a commander and a play style that lets you take advantage of powerful (and cheap) instants like Counterspell by leaving up mana each turn
So far I just add cards from new sets that fit the cube, but I'm not sure if they actually fit into decks
Although Wallys effect makes it solid for players, clearly he isnt in the same realm of popularity as Lillie or Acerola
This is very much a build-around Commander
Even some brushwork on the Xiphos (the sword) can be made to look like a Trident and he can be altered to a nice Aquaman