This is level 41 of the Main tunnel.
Whoo-hoo! You have now got the Lizard! Oh, wait, if you're reading this while playing the level and you clicked the Lizard on the 'Choose Your Character!' cutscene, you'll find yourself on a bluish level called B-1. So if you did click the Lizard, pause the game, go to the map, and find and click Level 41, and switch to the Runner.
Hey, the tunnel's turned orange! Despite this being the point where the Lizard is unlocked, we still recommend the Runner. There are lots of crumbling tiles, so you need to get back on normal tiles, fast! It's quite a long level, so just spend less time on the crumbling tiles and you should win.