Steparu has a video where it shows that all the buff can stack.
Thank you very much for all the information.
Do you know about the attribute on swell body that increases matk and slows movement speed?
I am wondering if this effect is exclusive to the enemy or if enlarging yourself will grant you 60% more matk and the speed reduction.
Gahaha! Hilarious stuff! Those enlarged shields covering the whole body pretty much.
And whoah, Centurions can dash and everyone in formation moves at their speed? Neat 0.o" (or was it a cronomancer buff thereā¦?)
From what I could see, the whole formation stayed in stepped and sped up with the Centurion independent of Haste.
Otherwise, the Cent would have left everyone behind if they didnāt move at sprint speed along with him. 
Hmm~ Interesting, so what if you were a cataphract/centurion, got a mount + movespeed buffs and set up formation? would everyone move about at lightning speeds? haha, well, I guess im deviating a bit from the main topic here. xd
Nowā¦ if only Swell body was usable on Summonsā¦ thatād make a nice class synergy there, heh, otherwise I see no point in getting the movespeed decrease attribute beyond level1 (unless it stacked the slow until 75%, which would be a huge penalty 0.o)
This would seem quite potentially abusable by coughtrollscough enlarging archer-like mobs for the +60% damage, heh.
I donāt know how formations would work with the Cent on a mount using trot, I havenāt seen anything like it. Judging by how sprint works in the video, I would speculate itās the same. Moving an entire formation based on your own personal speed sound great imo and makes a Cent that much more valuable in party play. I just donāt see a Cent, no matter how fast they are, leaving itās own formation behind.
Does Enlarge/Shrink work on bosses?