The standard: Sir Reginald, 64×96, 15 colours, dark scheme — now with his 4-frame walk, bold outline and brighter inside (watch him go)
GBA-compact sprites from any picture: shrink it right down, lock it to a tiny palette, get a true-size PNG (often under 2 KB). Everything runs in your browser — no server, no GPU.
Every sprite gets a bold dark outline with gentler inner lines and a brightness lift — defined, not murky — so it reads clearly on a small screen.