Since the Focus Beret got added in to Round 1, I would like to make some suggestions for it.
For some reason the hat is really REALLY focused on buffing Fallen Empire and only Fallen Empire. I would like to see it actually have more of a benefit to combo builds in general. Also, it's really not that difficult to get the timing for Fallen Empire after Dragon Combo, so I'm not sure why it was picked as an auto-cast.
So, on to the ideas...
Increase damage with Dragon Combo, Fallen Empire, and Sky Blow by X% (I don't know what's a good percent, so I'll leave that to the people who know)
Every X points in AGI increases ATK by X
If Dragon Combo is mastered, increase ASPD by X or X%
If Dragon Combo is mastered, increase damage of Sky Blow and Fallen Empire when used after Dragon Combo by X%
If base AGI is 100 or higher, increase damage of Raging Trifecta, Quad, Thrust, Dragon Combo, Fallen Empire, and Sky Blow by X%
If base AGI is 120 and headgear is +9 or higher, adds an X% chance to gain X% of damage dealt as SP (Combos are extremely SP intensive, and combo build can't afford to invest a lot in INT).
If base AGI is 120 and headgear is +9 or higher, reduce SP consumption by X%
If equipped with a Knuckle type weapon, increase ATK by X% and ASPD by X or X% (Not sure if this is possible, but it's worth looking at)
Increases damage of Crescent Elbow by X% (Have to have Sky Blow to unlock it, so it's technically part of the Combo tree)
I'm not suggesting all of these get put on the hat. They're just ideas that were running through my head that I think could be good options. I'd really appreciate your thoughts and opinions, since no one has really talked about the Focus Beret.