Nobody uses shadow spells (unless it's leviathan or sire).
Nobody uses smoke spells.
Only blood (healing) and ice (freezing) are useful for PvM, but only ice is used in PvP.
The others could be tweaked to make them a bit more viable for PvP instead of just sitting there collecting dust.
For example:
Nex's special attacks
Choke: Drains two prayer points per every two ticks, and drains stats based on the player's highest attack bonus. Smoke barrage in addition to poison could have a stat draining effect, the duration/amount drained can be reduced by wearing a facemask. The stat drain effect wouldn't stack if multiple people use the spell on a single target. There could also be a smoke inhalation effect that puts a cloud over the target's face that deals damage over a few ticks which cannot be mitigated by drinking an antipoison, only reduced by wearing a facemask.
Embrace Darkness: The chamber will be darkened drastically. The closer players are to Nex, the darker the room will be. If players stand next to Nex for too long, they will take constant damage from the pure shadow. Shadow Barrage or Blitz in addition to stat drain could have a similar effect of darkening the players screen and doing unavoidable incremental damage while the effect is active and the closer the target is to the player, the amount of damage taken reducing as the target moves away.
Shadow Smash: Deadly shadows will appear under every player. Players have three ticks to move out of their way before they erupt and deal up to 50 damage. Shadow Barrage or Shadow Blitz could have a chance of opening up a black hole beneath the target which deals twice the amount of damage if the target doesn't move away in time (e.g. you could freeze them in place with ice barrage/blitz then Shadow Blitz them).
I'm sure there's so many other forgotten spells out there but that's all I can fit in one post. Thanks for reading.