Remove black screen between waves.
60 seconds for 10th wave boss is short time (stop timer on boss wave)?
Small crocodiles in 1st waves should be pets.
Are there 12 waves in total per 1 entry with energy? 12 fireplaces

In general 9 waves are easy, 10th is huge jump (i was alone warrior with 3 average rogues - 60 seconds is short time i guess).