If you could make one balance change to every class on P99:

[Vexenu]

This list attempts to balance the classes by making the most minimally invasive but still impactful changes.

Wizard - Add Clarity line of spells (buff)
Magician - Add a spell to summon root nets (buff)
Enchanter - Remove Clarity line of spells (nerf)
Necromancer - Revert unclassic nerf to life tap resists (buff)
Shaman - Torpor now applies mana drain to target (nerf)
Druid - Add new level 51 spell, a slow scaling from 30% up to 40% at level 60. (buff)
Cleric - Can now summon single charge, lore, tradeable, no rent rez totems (buff/QoL)
Warrior - Add 'Weapon Attunement' combat ability at level 40, 20 sec CD, guarantees proc on next attack (buff)
Monk - Implement Luclin-era AC adjustment (nerf)
Rogue - Add unique Rogue-only tradeskill to craft tradeable masks with charges of various illusions (buff/QoL)
Paladin - Add innate group heal proc that scales with level on all attacks (buff)
Shadowknight - Add innate life tap/mana drain proc that scales with level on all attacks (buff)
Ranger - Add Druid Ring spell line of self-ports (buff/QoL)
Bard - Add Melody (buff/QoL)