Cool ! All I tested was the absorb HP/MP one (doesn't work).
I ran quite a lot of tests today, regarding the byte at 0x02 for the type of damage / attack modifier.
Here is a quick recap of what we already know, and what I've discovered. All of these work :
00h: Inflict the weapon's status on characters without doing damage. Miss enemies.
11h: Deals physical damage
22h: Deals magical damage
23h: Deals %damage based on the target's CurrHP. I think Weapon Attack is the percentage (10h=50%, 20h=100%, etc)
24h: Deals %damage based on the target's MaxHP.
26h: Deals constant damage (Magic Hammer, 1000 Needles, ...). 01h = 20 HP/MP.
28h: Fully recovers the target's HP/MP (Mog Dance).
29h: Always deals 1 damage (?).
60h: Damage = attacker's current HP (White Wind)
61h: Damage = MaxHP - CurrHP (the
? enemy skill)
68h: Random Damage (Dice)
69h: Damage = number of times the party escaped (Chocobuckle).
6Bh: Damage = (hours played * 100) + minutes played (Time Damage)
6Dh: It's Aire Tam Storm's damage calculation method, meaning that it always deals 0 damage since enemies can't equip materias
96h: Damage = approx. 1/2 attacker's current HP
...And one I'm not sure about :
6Ch: It's Everyone's Grudge damage calculation method, but it doesn't seem to work, as even after killing some enemies, your weapon still deals 0 damage. I didn't check if it takes into account the number of deaths
in the player's party, though. Thanks to anyone who can test this.
Most of the others don't seem to work or to be interesting. I'm too lazy to list the Ultimate Weapons' special effects ; they're in the wiki anyways.