You can easily reach a x50 combo in the first combat challenge, "Intensive Training". Enemies will not have armor or shields in this challenge. Reach Round 4 so there are enough enemies to build up a x50 combo. To ensure you do not get hit while fighting, perform a standard strike, then jump over an enemy, and repeat. None of the enemies will be able to hit you. It takes a little longer than countering and fighting the normal way, but it is much safer and easier to do. Do not perform any combo attacks or finishers -- so the enemies stay alive longer. If you have already unlocked the Shock Gloves, activate them to get a x2 multiplier with each hit.