It's easy to mix up Sonic's darker variants. Here's the cheat sheet: Super Sonic is the canonical heroic transformation (gold fur, red eyes, Chaos Emeralds); Dark Sonic is the anime-only rage form (black fur, white pupils, purple aura); and Sonic.exe is the fan-made creepypasta horror character (black fur, red pupils, sharp teeth, blood drips).
If you're choosing a printable for a kid, Super Sonic is the most universally safe pick. Dark Sonic is the middle option — intense but heroic. Sonic.exe is for older fans only.
A fourth variant has been growing fast in fan circles: Sonic.exe Magic, which pairs the creepypasta Sonic with summoning circles, spellbooks, and cursed Chaos Emeralds. If your kid is past Dark Sonic but not quite ready for full-on creepypasta gore, Sonic.exe Magic is a great middle stop.