level 19 "straightjacket" is the most unfair and hard IMO. You need to depend on vertical spawns and then stick a flower on the outside of the "tubes".
I made a few hard levels too for the "Prolific" mode. Currently there are 44 random levels that can be selected but I'm about to patch in 16 more in v1.01 this weekend :D
(EDIT: this week of the 28th)