I beaten this level with the trap booster as my consumable. The traps I used were the spinblade, the spring trap, and the barricade. I use the barricades to force all enemies to the bottom path, then used spring traps to spring the enemies into the lava pits and spikes. I put the spinblades on the very next tile after a spring trap to keep the enemies on the spring trap as long as possible. I didn't need to on this level, but if you have to, pause the game using the tab button, and then place a barricade over any enemies that slip through the traps.

Thanks for the advice! I'll give it a try.
I was using spring traps / Demon / Barricades and also trap booster as consumable, but the demons wasn't good enought to hold the thieves.