Is supergemming possible in Gemcraft Labyrinth?
For Gemcraft Labrynth, supergemming is still possible. From the wiki:
Since GCL red gems have the ability to incease their attack damage dramatically by killing enemys. So they are the best for supergemming.
How to do exactly:
First get a strong red gem and place it in a tower. There should be no other things that can kill enemys but this one red gem so it gets all the kills. This will lead to enormous damage values. Support the red supergem with (up to 8) amplifiers that contain further red gems to incease the impact of its ability. To anger the incoming waves is also important because it will cause more enemies what will lead to more kills for the gem to incease its damage value. The supergem can also be mixed with other colors if you want. Best combination is red-lime-yellow because it hits multiple enemys with the multiple amount of its huge damage value. The normal way of supergemming can still be used to incease the damage and speed further.