I've come up with some challenges for the Classic Sonic games. Here they are:

Sonic the Hedgehog 2: Sonic Labyrinth Edition

The point of this challenge is this:

Sonic cannot run fast in this challenge, meaning that the only way to go fast is by getting Super Shoes and Spin Dashing. The only way to run again (just like in the original Sonic Labyrinth) is by getting all 7 Chaos Emeralds.

This can ONLY be done with Sonic. No one else.

You CANNOT use the Chaos Emerald Trick to automatically get all 7 Chaos Emeralds. If you do, this counts as an immediate failure for cheating.

NOTE: This challenge can also be done on Sonic the Hedgehog 3 and Sonic & Knuckles.

"Hyper" Sonic till the end

This challenge takes place in Oil Ocean Zone Act 2.

When you first go into the stage, activate the "Hyper" Sonic glitch, and keep the glitch active until the boss had been beaten. You can also do this challenge when all 7 Chaos Emeralds have been collected. Activate the glitch, and collect 50 rings while keeping that glitch active. Then, turn into Super Sonic. Now, complete the stage while keeping the glitch active with Super Sonic.

End of Challenges

Can anyone else help me think of more?