First of all, I don't know where I can post this, and I don't know if there's a post like this before.
On PS2I managed to crack up all of MUA2 PS2 files and gather them up in one RAR, called 'MUA2 PS2 Assets'

After that, I've tried to experimenting with the files, and find these discoveries :
1. Fusion classes and new power classes that confirmed to be
working on MUA : (
Proof Of Concept : My Malice's (Sue Storm) Dome Blast power - available on my workbench) class = pulltome (taken from Spiderman's Web Warrior power)
class = vacuum (taken from 'Collect and Smash' or 'Collect and Blast' fusions)
They will be working if you use this handler on the powerstyle :
handler = ch_grab_hold_base2. We
can use textures from MUA2. (
Proof Of Concept : My Songbird's Eagle Dive effect - available on my workbench) Texture that confirmed to be
working is
speed7_clamped.igb3. Fusions defined in this file called
power_fusion_matrix.xmlb (this can't be used in MUA, though. Maybe there's a little chance on it to be working on MUA).
4. There's a new couple lines regarding fusions in the
shared_anims.xmlb ea_allyoop_end = fusion_ally_oop_end ;
ea_allyoop_start = fusion_ally_oop_start ;
ea_allyoop_throw = fusion_ally_oop_throw ;
ea_attack_projectile = fusion_attack_projectile ;
ea_attack_split_finish = fusion_attack_split_finish ;
ea_attack_split_start = fusion_attack_split_start ;
ea_blast_tornado = fusion_blast_tornado ;
ea_clothes_left = fusion_clothesline_left ;
ea_clothes_right = fusion_clothesline_right ;
ea_clothes_start_left = fusion_clothesline_start_left ;
ea_clothes_start_right = fusion_clothesline_start_right ;
ea_create_ball = fusion_create_ball ;
ea_create_object_split_finish = fusion_create_object_split_finish ;
ea_create_object_split_start = fusion_create_object_split_start ;
ea_create_projectile = fusion_charge_projectile ;
ea_create_tornado = fusion_create_tornado ;
ea_create_vortex = fusion_vortex ;
ea_end_tornado = fusion_end_tornado ;
ea_ground_pound_finish = fusion_ground_pound_finish ;
ea_ground_pound_start = fusion_ground_pound_start ;
ea_hammer_end = fusion_hammer_end ;
ea_hammer_loop = fusion_hammer_loop ;
ea_hammer_smash = fusion_hammer ;
ea_hammer_start = fusion_hammer_start ;
ea_hold_tornado = fusion_hold_tornado ;
ea_knockdown = fusion_knockdown ;
ea_knockup = fusion_knockup ;
ea_manjectile_end = fusion_manjectile_end ;
ea_manjectile_loop = fusion_manjectile_loop ;
ea_manjectile_spin = fusion_manjectile_spin ;
ea_manjectile_start = fusion_manjectile_start ;
ea_run_in_ball = fusion_run_in_ball ;
ea_throw_ally = fusion_throw_ally ;
ea_vortex_blast = fusion_vortex_blast ;
ea_vortex_melee = fusion_vortex_melee ;
ea_zone25 = power_fusion ;
5. There's a couple lines regarding fusions in
shared_event_templates.xmlb aswell :
event {
name = power_fusion_start ;
type = ce_power_fusion_start ;
}
event {
name = power_fusion_finish ;
type = ce_power_fusion_finish ;
}
event {
name = fusion_collection ;
type = ce_fusion_collection ;
}
6. There are more new events powerups regarding powers and fusions in the
shared_nodes_combat.xmlb file.
That's from PS2.. Now we go to PS3..
On PS3Sadly, I just found only two discoveries..
1. Each character's effects, powerstyles, talents, and fusions are packed into a .PAK file. Until now, there's no extractor that can extract MUA2 PS3 files. Can't be opened with WinRAR.

But, there's a couple lines at the bottom of the file that
readable. Open it with Notepad, BTW

These are the examples :
-
jeangrey_fightstyles.pak :
data\talents\jeangrey.xmlb data\fightstyles\interact_jeangrey_victim.muc data\fightstyles\fightstyle_default.muc data\powerstyles\ps_jeangrey.muc packages\generated\characters\jeangrey_fightstyles.pkgb data\fightstyles\moveset_flying.muc data\fightstyles\interact_grabvictim.muc
-
jeangrey_fusioncreatetornado.pak :
effects_igx\base\misc\target_control_tornado.igz materials\effects\misc\fxt_sm3_ring_3.igz materials\effects\decals\fxt_crack08_s.igz effects_igx\char\jeangrey\jeangrey_f_to_create_blast.igz materials\effects\misc\fxt_gradient02_d.igz materials\effects\glows\fxt_lightshaft_d.igz materials\effects\glows\fxt_phoenix_trail_d.igz models\effects\common\common_white_sphere.igz effects_igx\char\jeangrey\jeangrey_f_to_create_power.igz packages\generated\fusion\jeangrey\jeangrey_fusioncreatetornado.pkgb materials\effects\models\penance\penance_tornado_ringblack.igz materials\effects\decals\fxt_crack04_d.igz data\fusion\jeangrey\jeangrey_fusioncreatetornado.muc materials\effects\misc\fxt_sm3_whitefaulta_35.igz materials\effects\decals\fxt_crack04_n.igz effects_igx\base\misc\target_control_lockon.igz materials\effects\distortion\fxt_distort_shockwave.igz
2. There's a
'shocking' file called
permanent_pc.pak. Can you imagine? They have been working on a PC version. Why they're not release it as a PC version?
BTW, this is the lines from that file :
packages\generated\maps\package\permanent_pc.pkgb textures\ui\hud_pc.igz
On the above, the file contains two files :
1. packages\generated\maps\package\permanent_pc.pkgb, I'm not sure about this one..
2. textures\ui\hud_pc.igz, Positions of the HUDs on PC version? I'm not so sure..
Just realized these, although I'm not so sure about the functions of each format :
1.
.xmlb (Fightstyles, and talents are formed with this format. Ex: data\talents\jeangrey.xmlb)
2.
.muc (Fightstyles, and powerstyles are formed with this format. Ex : data\fightstyles\moveset_flying.muc data\fightstyles\interact_grabvictim.muc data\powerstyles\ps_jeangrey.muc)
3.
.pkgb is for packages for each characters. MUA compatible, maybe.
4. Animations are stored (and formed) into a
.hkx file (God, another unknown format -_-) Ex : anims\123_jeangrey_4_conv.hkx
5. Materials (like debrises, chunks, etc.), models, and almost all effects (powers, fusions, and misc. effects) are stored (or formed) into an
.igz file.
6. There's a mention about an .igx format somewhere..
Gameplay Differences on NDS, PSP, PS2, WIIPlayed all the games
on emulators and actual consoles (I bought all the games for their respective platforms

Some of them are borrowed from my friends)
On PSP :
- Fusion sounds is triggered right when the fusion is near the end of the fusion. (You can call it late)
- Camera movement is not always 'moving as they were intended' when using Fusions (Sometimes the camera move closer to the characters that are doing Fusions, sometimes it's not.)
- Music are sometimes can be heard throughout the gameplay, but sometimes it can't.
- Low-Resolution graphics, but medium quality sounds
- Lagging (a bit), Graphical bugs and glitches. (Low to med in emulator, low in actual console)
- Loading time is a little bit longer.. (Am I the only one who experiencing this?)
On PS2- Fusion sounds
sometimes triggered right when the fusion is near the end of the fusion. (You can call it late)
- Camera movement
sometimes but not so often 'moving as they're intended' when using Fusions (Sometimes the camera move closer to the characters that are doing Fusions, sometimes it's not.)
- Medium Resolution graphics, and low quality sounds XD
- Lagging, Graphical bugs and glitches. (medium in emulator, low/none in actual console)
- Crash a lot on emulator, but not so often..
On WII- Fusion sounds is triggered right when the characters are doing their fusion.
- Camera movement is 'moving as they're intended' when using Fusions.
- Medium to High Resolution graphics and high quality sounds.
- No graphical bugs and glitches. (Both in emulator and actual console)
- No lag
On NDS :
- The fusion type on the NDS is different. It seems like two characters releasing Xtreme powers at the same time, rather than they incorporate their powers to create different powers for fusions..
- No problem at the fusion sounds, camera movements, etc.
- Low-Resolution graphics and low quality sounds (yeah, NDS

)
Keep in mind that 'emulator gameplay' is affected from your computer.. Not all gamers experiencing the problems above, but at least I do.. XD
Conclusion : The most stable version of Marvel:Ultimate Alliance 2 game is
WII Version! 