Return to Answer

You have listed a very specific criteria, and unfortunately, I doubt if there is actually one single idiom to describe all of that. One could possibly use a combination.

For "doing too much" :

Burn the candle at both ends.
Bite off more than he can chew
Carrying it too far.

For "illegal" :

You'll be caught red-handed
Taking the law into his own hands.
Fool's errand

For "impossible":

Flogging a dead horse. Nailing jelly to a wall
Mission impossible

I would suggest, if you were to want a sentence expressing all three of your criteria, something like this:

You can't catch lightning in a bottle(impossible), besides, you'd probably be caught red-handed(illegal), and end up trying to burn the candle at both ends(do too much)

You have listed very specific criteria, and unfortunately, I doubt if there is actually one single idiom to describe all of that. One could possibly use a combination.

For "doing too much" :

Burn the candle at both ends.
Bite off more than he can chew
Carrying it too far.

For "illegal" :

You'll be caught red-handed
Taking the law into his own hands.
Fool's errand

For "impossible":

Flogging a dead horse. Nailing jelly to a wall
Mission impossible

I would suggest, if you were to want a sentence expressing all three of your criteria, something like this:

You can't catch lightning in a bottle(impossible), besides, you'd probably be caught red-handed(illegal), and end up trying to burn the candle at both ends(do too much)

For "doing too much" :

Burn the candle at both ends.
Bite off more than he can chew
Carrying it too far.

For "illegal" :

You'll be caught red-handed
Taking the law into his own hands.
Fool's errand

For "impossible":

Nailing jelly to a wall
Mission impossible

You have listed a very specific criteria, and unfortunately, I doubt if there is actually one single idiom to describe all of that. One could possibly use a combination.

For "doing too much" :

Burn the candle at both ends.
Bite off more than he can chew
Carrying it too far.

For "illegal" :

You'll be caught red-handed
Taking the law into his own hands.
Fool's errand

For "impossible":

Flogging a dead horse. Nailing jelly to a wall
Mission impossible

I would suggest, if you were to want a sentence expressing all three of your criteria, something like this:

You can't catch lightning in a bottle(impossible), besides, you'd probably be caught red-handed(illegal), and end up trying to burn the candle at both ends(do too much)

Several for "impossible":

Nailing jelly to a wall
Mission impossible

For "illegal" :

You'll be caught red-handed
Taking the law into his own hands.
Fool's errand

For "more than he can do" :

Bite off more than he can chew
Burn the candle at both ends.
Carrying it too far.

For "doing too much" :

Burn the candle at both ends.
Bite off more than he can chew
Carrying it too far.

For "illegal" :

You'll be caught red-handed
Taking the law into his own hands.
Fool's errand

For "impossible":

Nailing jelly to a wall
Mission impossible