Deviantart open art creators:
https://danielmania123.deviantart.com/
https://glitchythehedgehog91.deviantart.com/
https://retrobunyip.deviantart.com/
https://gftheplayer.deviantart.com/
https://sonichex.deviantart.com/
https://thomasthehedgehog888.deviantart.com/
https://thomasandsonicyt.deviantart.com/
https://souptaels.deviantart.com/
https://thegoku7729.deviantart.com/
https://joshthehedgehog33.deviantart.com/
access to the Mystical Forest Zone Archives:
https://web.archive.org/web/20131208004009/http://themysticalforestzone.com/Sprite_section.htm
dream forest zone:
https://sites.google.com/view/dreamforestzone/home
full sheet of the explosions used in the dash engine and sonic worlds by Hex :
https://i.imgur.com/uIKUGo8.png
useful sprites from other not sonic related games:
https://www.spriters-resource.com/genesis_32x_scd/sockettimedom/
Sonic Mania sprites:
https://www.spriters-resource.com/pc_computer/sonicmania/
Sonic Custom Sprites:
https://www.spriters-resource.com/.../sonicthehedgehogcustoms/
Sonic 3 sprites:
https://www.spriters-resource.com/genesis_32x_scd/sonicth3/
Sonic & Knuckles sprites:
https://www.spriters-resource.com/genesis_32x_scd/snk/
Sonic 2 sprites:
https://www.spriters-resource.com/genesis_32x_scd/sonicth2/
Sonic CD sprites:
https://www.spriters-resource.com/genesis_32x_scd/sonicthehedgehogcdsegacd/
Sonic 1 sprites:
https://www.spriters-resource.com/genesis_32x_scd/sonicth1/
Sonic Spinball sprites:
https://www.spriters-resource.com/genesis_32x_scd/sonicspin/
Knuckles Chaotix sprites:
https://www.spriters-resource.com/genesis_32x_scd/knuckleschaotix32x/