Sinking Feeling (Quick Sand Brutality) does work, I tried it repeatedly on the first few days and couldn't get it, but then I accidentally did it the other night and have been able to do it consistently ever since... I believe the TRUE requirements are something like this:
- Must hit with 3 special canceled Quick Sands
- Final hit must come from Quick Sand
OR
- Must end 3 combos with Quick Sand
- Final hit must come from Quick Sand
OR
- Must hit with 3 Close Quick Sands
- Final hit must come from Quick Sand
Because after I started more frequently comboing into Quick Sand I've never failed to perform the brutality when I try to.
Brutalities I've unlocked:
The Klassic (Uppercut) - uppercuts head off
Pulled Apart (Dangerous Chronology Kombo) - rips leg off
Trapped (Sand Trap) - removes their legs in the sand, lifts into the air and smashes with sand hammers
Sinking Feeling (Quick Sand) - Lift them out of the sand and break their neck, eyeballs pop out in the process
Stick It Out (Toward Throw) - smash them into the floor, destroys head/upper torso, lower body and arms remain, as a side note I can't seem to perform this one but I've seen my Geras AI do it two or three times, so I'm guess the requirements aren't listed correctly
Not unlocked, but I know they exist:
Back Throw - crushes their body between sand hammer & anvil
Titan Tackle - run them into sand wall and then destroy their head with big fist
Temporal Advantage - ??? (my brother unlocked it, never seen it performed)