It just occurred to me that Magic causes NO back attack damage. I can't believe that it took me this long to realize that. The attack needs to be physical and the target goes to all battle participants. I changed Comet2 to have a Damage Base of 11h (physical), Strength of 3, target to 47h (multiple, both sides, same as both Sewer Tsunamis), 0x12 to 04h and 0x13 to 0 and my party took around 1050 avg dmg while the enemy party I was up against took about 875 avg dmg. I changed Comet2's 0x13 to 1 and my party took around 560 avg dmg and the same enemies took 1900 avg dmg.
So 0x12:04h DOES work, but only if the attack is physical. Target may not necessarily have to be 47h. Description is: "Causes back attack damage (physical only) to target in row ". I'm guessing caster's row is always row 0.
I've been screwin' around with Damage Base (as it will now be called as that's what it really is) and I think I have identified 47h and 50h. 50h at least, causes no damage calculation (not even a miss or 0) and is used in quite a few magics that change statuses. 47h has the same damage calculation as 37h, but is Magic. Both 37h and 47h ignore Barriers so they should be thus:
37h: Physical Damage [Strength x 16]; ignores Barrier
47h: Magical Damage [Strength x 16]; ignores MBarrier
50h: No Damage Calculation
Def Ignoring is completely different. Pandora's Box is Def Ignoring, but MBarrier still protects against half the damage. Def Ignoring will ignore the target's Def and MDef stat. Even with these values, however, there is still the random variance ([224..255]/256 or so) that the attack is multiplied by every time. Only 26h skips the random variance and M/Def status. If an attack/item were set to 37h and Def Ignoring, it would act the same if it were, instead, set to 47h and Def Ignoring.
Effects: 01h, 02h, 03h, 09h, 16h, 17h.
Just tested 01h. If the attack attempts to inflict death, but the target is immune, then it "summons" Gunge Lance.
Just tested 02h. The attack randomly "summons" Fat-Chocobo.
I say "summons" because this gets tricky. Fat-Chocobo's animation is 10h for SUMMONS. If a Magic attempts to "summon" Fat-Chocobo, the battle engine will read the data on the Fat-Chocobo attack (except it keeps the original target(s)) as a Magic and perform animation 10h (MBarrier). The same thing would probably happen with Items (10h is Smoke Bomb) and E.Skills (
?). The same sort of thing happens to Gunge Lance. The camera just freezes in most cases when these happen, however.
Choco/Mog gives the Modifier 0x13 a value of 15. This is probably the chance that it will summon. I'm not sure what it's out of, but it seems that even at 15 it rarely happens. I must have cast Bio 20 or more times in one battle trying to get it to summon Fat-Chocobo. It might just be straight-up percent.
I haven't even touched 09. I tried a few attacks with 16h and 17h, but couldn't get any results.
0Ah, 0Bh, 0Ch, 0Dh,
, and 1Eh - 22h. These are not used anywhere in the game, but they exist in gaps between other known effects. Do they have any purpose? Probably not. I'm likely to ignore these, but if someone wants to test them, go for it.
Oops: 1Ah is Blade Beam's. It's "perform attack  on targets not targeted". I made Fire perform "Knights of Round" (not "Ultimate End". Again, it's using the attack data's names as well since Summon attack names are stored elsewhere.) on 5 out of 6 battery caps. However it has the same animation issue as 02h has in that it will use the animation index of the Magics and not summons and this attack looked like Barrier.
The 0002h property. I have no clue what it is. I thought it might be related to pausing ATB, but it doesn't seem to have that effect. ATB pauses on "wait" mode whether or not that is checked.
Also, what effect does Blade Beam property have? I know it's the only attack that uses it and I thought it might be something like "target becomes caster" or "maintain individual animation for multiple targets", but those don't seem to be correct.
I think these are the last unknowns. If I can get some help flattening out the unknown parts of these then this will be ready for version 1.0!
EDIT: Once again I updated this with the new descriptions. I also re-did the Weapons tab because the element information was limited. I removed the limitation. Until now, you could only have one element on your weapon. Now you can have as many as there are. I don't know why exactly I did it that way to begin with, but now you can make the Buster Sword do Fire, Ice, and Bolt Damage.
Other Properties were changed from their values to simply "unused". No attack in the entire game uses them, but I'll keep them there in case anyone wants to play with them. Ya know, try to cause crashes or something.
Menu restraints in the upper left were re-done. Seems that everything that shows up in the out-of-battle menu shows up in the in-battle menu. So the "Appears in Battle Menu" was changed to "Sellable" (which is what I figured it was since beginning this).
I JUST noticed a (rather embarrassing) typo in the Attack Damage selection. Ignore it for now. I'll fix it in the next version. It's not worth a re-upload.
RE-EDIT: I screwed around with 0x12:13h (On Tifa's LBs) a little yesterday and got some strange results. I set Fire2 to that effect expecting it to give me a slot and when Vincent cast it he transformed into Death Gigas! I didn't lose control over him though. That was weird. I told him to attack the only enemy left and for a while I thought it froze, but he went through an entire idle animation loop beginning after the loop I commanded him on ended, appeared in front of the enemy, performed another entire idle animation loop (maybe two), the enemy just took damage as if hit (but DG didn't move), went through ANOTHER idle animation loop or two, went back to his position in line, performed MORE idle animation loops then the battle ended. Very weird. I've been afraid to test it with another character.
Speaking of Tifa's LBs, I've currently got Damage Base B1h set to "Based on Slot (Hit/Miss/Crit)". While this is true for Tifa, it's not exclusive to her. JENOVA*Birth's attacks all have this Damage Base as well. TFergusson states that it cannot critical. That makes a lot of sense. You wouldn't want Tifa's LBs critcal-ing on their own since it's based on the slot wheels. So I'm changing the description to:
"B1 Physical (Base * [Strength / 16]); No random criticals"
Either that or 11h must become "11 Physical (Base * [Strength / 16]); Allow random criticals" since 37h doesn't critical either.
I also noticed that since Blade Beam itself calls upon attack 7Ah that the attack in KERNEL.BIN must be the blade beam shockwave. So I'm changing its name from Braver to Blade Beam Wave and truncating the rest because they aren't really Cloud's limits. There will be an update soon with these corrections.