Luminatus
http://i21.photobucket.com/albums/b264/testaments/testament.jpg
From the end of game database in Xenosaga Episode III:
"They are the post-death form of Kevin and the others'; however they are not reincarnations, but beings who have slipped the bonds of normal space - their bodies. They can exert their abilities by accessing normal space from inaginary space (their consciousness) and controlling its physical phenomena at will.
By controlling physical phenomena, they also act directly upon the perception of those in normal space; you could see them as if they were actually there, even though your retinas would not be receiving any photons."
From the XenosagA 3 Perfect Guide:
<<The Power of Testament>>
　　　　The power of testament has no material limitation. Because they exert an effect on the real number domain from the imaginary domain, it is possible to produce an action that disregards physical laws. However, this miracle-like phenomenon is still just something that is performed only in the imaginary and real number domains within the lower domain, and is not something connected to the upper domain where U-Do exists.
"
http://translations.xenotensei.com/Xeno3/PerfectGuide.html
For actual feats, from the Summary of Xenosaga Episode II that is in EP3:
"The Patriarch laughed at them, calling them nothing more than insects and moved to destroy Second Miltia to demonstrate his god-like power."
QKImpZ3jdN4
Testaments easily shut down and wiped out a planet-destroyer.
I'll add more when I have the time.
From the end of game database in Xenosaga Episode III:
"They are the post-death form of Kevin and the others'; however they are not reincarnations, but beings who have slipped the bonds of normal space - their bodies. They can exert their abilities by accessing normal space from inaginary space (their consciousness) and controlling its physical phenomena at will.
By controlling physical phenomena, they also act directly upon the perception of those in normal space; you could see them as if they were actually there, even though your retinas would not be receiving any photons."
From the XenosagA 3 Perfect Guide:
<<The Power of Testament>>
　　　　The power of testament has no material limitation. Because they exert an effect on the real number domain from the imaginary domain, it is possible to produce an action that disregards physical laws. However, this miracle-like phenomenon is still just something that is performed only in the imaginary and real number domains within the lower domain, and is not something connected to the upper domain where U-Do exists.
"
http://translations.xenotensei.com/Xeno3/PerfectGuide.html
For actual feats, from the Summary of Xenosaga Episode II that is in EP3:
"The Patriarch laughed at them, calling them nothing more than insects and moved to destroy Second Miltia to demonstrate his god-like power."
QKImpZ3jdN4
Testaments easily shut down and wiped out a planet-destroyer.
I'll add more when I have the time.