Most of our sprites are in what we consider a final form, and are free for the community to improve the animations of. However there are a few that we're still doing a couple last-minute tweaks to, and which should be avoided:
Human Footpad - base frame is done, animations are in-progress
Human Highwayman - etc.
Human Thief/Rogue - need their legs/skin/feet redone, and need an animation overhaul. Nothing done.
Human Poacher Line - Whole line needs some minor tweaks to their appearance, nothing done.
Human Cavalry Line - minor tweaks to the base appearance to make the horses much bigger.
Human Horseman Line - etc.
Goblin Direwolver and Pillager - need remakes of the base appearance; almost done.
Great Troll - eternal and tsi are working on a redesign.
All Elves - need some minor tweaks to clean them into "pure pixel art", and need an animation overhaul; most of the base sprite redesigns are done.
Fire Dragon - need some basic respriting; eternal is working on a base frame for the Dragon.
Cuttlefish - needs to be resprited.
Ancient Lich - Eternal may be working on a new base frame.
Armageddon Drake - needs a redesign to match the current drakes.
Most of our campaign hero sprites are bad frankensteins and could stand to be updated:
Delfador's Memoirs - needs a new Wose Shaman
Descent into Darkness - needs a less-obviously-frankensteined main character, and a better sprite for the frontier baroness.
The Eastern Invasion - Needs a new horse unit, can probably be mainlined as a morning-star-using cavalry unit.
Liberty - Needs a new Shadow Mage line; being worked on by Fmunoz. Also needs a new death squire, should be frankensteined from the bits that made up the WIP death knight and mainlined from that. Skeleton Rider and bone knight should be made bigger and have the new skulls.
Sceptre of Fire - Needs a new caravan.
Son of the Black Eye - Needs new orc shamans; I remember seeing someone working on them on the forum.
The Rise of Wesnoth - Needs new sprite designs for Haldric and Jessica.
The South Guard - Needs a better Infantry Lieutenant; being worked on by Rhyging. Also needs a better horse-mounted character.
Under the Burning Suns - ... too much to even list. Needs as much work as all the other campaigns combined.