Reaper expectations

[Lyth]

It's likely to be a resource-based oGCD that builds up your transformation meter. The Gamer Japan interview that was translated on reddit states that the Avatar's (blobfang minion) appearance also changes as your meter fills.

During the reveal, they show your Avatar's attack animation on its own initially, and later when weaved with what seems like your main combo.

[MagiusNecros]

Only thing I see out of that interview regarding anything changing is player appearance upon transformation and that it'll differ slightly based on player race. There is nothing in there that says the demon changes appearance as your meter builds. The devs comments about multiple different demon models were really clear that they had to settle on one design and that they can't have multiple demons out at once due to system limitations.

Primarily because of Alliance Raids and places like Eureka/Bozja having a lot of players and the game can't handle that many models.

Plus it's very clear the demon is limited to oGCD and burst mode appearances unlike the pet/minion natures of SMN/MCH/DRK.

All Yoshi has really given clarity on is that it very much is going to be a builder spender job. Which will be different from Dragoon's gauge maintaining aspect.

[Reksanden]

All Yoshi has really given clarity on is that it very much is going to be a builder spender job. Which will be different from Dragoon's gauge maintaining aspect.

And out of the melee DPS, this makes it the most unique - at least, as far as we know. DRG and NIN maintain their gauges, MNK has a much simpler form of a gauge and doesn't quite count, and SAM builds gauge but spends it much more consistently, and more on a skill-by-skill basis.

If anything, the nature of building and spending like that sounds a lot closer to RDM, where it works just fine.

[Lyth]

...

"Eventually, I decided there should be an additional avatar/minion fighting for the player and its appearance will change as the special meter fills up."

Everything is subject to change, obviously, but Yoshi-p explicitly states this in the interview. You're right in that the Avatar seems to be functionally just a set of oGCDs, much like Edge/Flood of Shadow are presently on DRK.

How will your Avatar change as your meter fills? Well, he also states:

"When someone suggested a Chūnibyō-ish idea: a job where its power gets increasingly more intense as the battle goes on - the idea was immediately agreed by the whole team."

I suspect that the Avatar will become progressively more menacing and edgier as you build meter, until it takes over you and possesses you.