I like the general idea of having the ability to travel through walls with a penalty side effect like this. It might also be interesting if there were some “ghost walls” that you need to be solid to pass through or something like that – in a couple playthroughs, I found that even with the faster timer I could sometimes collect more items even while staying a ghost the entire time!
I think having a longer timer would help too, since the level is decently large I was never really able to collect more than 5-8 barrels. Overall, I think this game could be pretty fun with some polish!