We need backsprites, icons and concept art. Shinies are also being worked on, if you are interested in doing recolors.
In terms of what's actually needed:
(* means that we have a suitable placeholder if necessary, though it's not completely official yet)
(! means that it's needed for the demo)
Backsprites:
All backsprites are done. Thanks Reliability plus all the others who helped out!
Icons:
044/Inflare
045/Ingero
051/Grific
052/Gryphonic
056/Vixun
059/Kondria
063/Stribra
065/Harskrow
082/Zantilidae
084/Pythang
098/Slowpriest
103/Seraph
106/Abyssus
107/Equill
108/Tellure
121/Drakodo
129/Chiarame
130/Serberine
132/Engil
133/Benengil
135/Malduval
139/Brontogon
140/Blitzfaust
141/Vilephist
145/Sinestril
146/Malistril
154/Caribrisk
156/Tundrolf
157/Wolfrost
158/Reefrain
159/Polara
160/Polarice
162/Ferrian
165/Cackinge
177/Kraklaw
178/Leoracle
179/Khaphix
182/Allufang
183/Kunaiga
184/Purior
188/Thoraxa
189/Illumbra
190/Snarliger
191/Noctiger
192/Raiger
196/Kuranpu
198/Unicrown