Given that I was complaining to someone about how far too many of the later masks in G1 were overspecialised and thus completely useless in most situations (compare that with the original 12 masks), this will probably come off as hypocritical, but as long as people continue to beat the very dead horse that is G1, I might as well propose what the Nuva editions of some of the masks without Nuva forms are. This is in addition to what they do already.
Huna: Conceals user's shadow as well.
Rau: Allows user to instantly create and understand a language on the spot.
Mahiki: Allows illusions to be physical and audible, as opposed to just optical.
Komau: Allows user to make someone do something against their morals.
Matatu: Allows user to use telekinesis on things as long as they know they're there - no longer relying on sight.
Ruru: Allows user to absorb light from the surrounding to make things darker, allowing them to manipulate light levels for their purposes.
Jutlin: Allows user to make organic material decompose as well.
Avsa: Allows user to drain light and all that from a group of people.
Shelek: Robs target of all senses, as opposed to just hearing and the ability to speech,
Crast: Repulses more than one object at a time.
Mohtrek: Can summon future selves as well.
Felnas: No longer do you have to be touching your target.
Pehkui: Can now shrink other things.
Kualsi: Can travel to places nearby all around you, no longer needing to see them to travel to them.
Kiril: Can now repair organic materials as well.
Tryna: Keeps G1 Canon alive for much longer than it should be. Very popular Nuva mask.
Zatth: Summons an army of clowns in addition to the random summon to scare people into submission.