According to TCGPlayer's charts, the hyper rare version of Mega Charizard X ex from Phantasmal Flames has dropped a massive 49% since launch, while Mega Evolutions' Mega Luracio ex #188 and Mega Gardevoir ex #187 have fallen 29% and 19%, respectively
Calgar's ability is also better for getting cards than Greyfax's, as you don't need to faff around with getting a Clue token and paying even more to sacrifice it Calgar just gives you a draw instead
When recruiting mercenaries with Primera, this card brought to Primera can be used immediately under the premise that a monster is placed in the magic & trap zone, and it has no disadvantages other than synchro restrictions, so it can be seen as having quite high versatility
There are a ton of great artifacts in the set, including the Equipment cards with Job Select, and there are also a few different cards that care about artifacts like Rook Turret and Gaelicat, both of which are at common rarity
They can only be played in 4 of the total 32 all of which are three times less played than other colour combinations