A first time see. I was playing the most famous chinese map "The Dragon Slaughter". There are no cheats or special leveling script, Gem was level 108 and the next fight game me infinite leveling. I stopped clicking when I was level 1647 and shut the game.


Save just before:
Level 1647

Just move on the road, an automatic fight will occur and you will be either level 50 or infinite (1/2 chances). Reload if it gives you level 50 (I am using special script which bring any hero down to 50 if the experience is negative after battle.