Batman Universe:
James Gordon - Det. Bullock gotham mates
Damian Wayne Robin - existing robin parts
Red Robin
Talia al ghul - zombie wanda hair piece black cat chest or San Serif from The Spirit
Deadshot - Could use the gauntlets from the spider sense spiderman, regular red body
Black mask - regular suit
The Riddler - green suit from puppet master
Mad hatter - Alice in wonderland mad hatter
The clock king - regular brown suit maybe the old guys from the muppets
Hugo strange - could use the same hugo strange from the gotham mates
Mr freeze - mr freeze from the Gotham mates, blue head from the captain marvel movie krees or Nova Corps and with some modifications you can fit the helmet piece from the deep immersion spiderman Walgreens wave
Scarecrow - pumpkin king jack body, witch hat from same line
Hush - brown jacket from Det. Bullock gotham mates or future wolverine coat
Zsasz - regular skin chest piece
Superman Universe;
Metallo - first release silver surfer, with a modified hairpiece cut in half
Parasite - not too many purple chest pieces but maybe purple man
Mongul - this a tough one but truly needed
General zod - black body
Brainiac
DC universe;
Zatanna - jean dewolff legs,
Constatine - red tie from the spirit mates and brown coat from det Bullock gotam mates, cigarette from silent bob mate
Kyle rayner - existing green lantern
Black cannery - jean dewolff legs
Atom
Metamorpho - 1st release absorbing man
Captain Atom- silver surfer for body
Firestorm - human torch hair piece, ancient one body from dr strange movie
Mister miracle
Black lightning
Static Shock
Mister terrific
I could go on and on and on but that would be my wish list.