That's really the only item that I don't know how to generate / trigger the red bubble with yellow flashing pulse, Ive seen it as early as level 4,8,10,19,32 (alot of times throughout this competition!) but supposidly its randomly generated 1 in 4096 bubbles ? I have seen all three secret rooms (level 40 without dying) a total of three times. Ive gotten 2.5mil,2.6mil, and 2,850,410. Id really like to cap off in 3mil pt. range.. but I might have reached my pt. peak.
My own personal strategy;
As far as pts. go ive come to realize that you shouldn't grab the umbrella's that skip you 3,5, or even 7 levels just to try to get to the secret rooms. Those 3-7 levels can get you tons of pts. Also sometimes spelling extend although gives you an extra life can cause you to lose the maximum pts. on a particular level, so before grabbing that last letter that you may need to complete it, think about not popping it. Also for me personally if I get the shoe it's bad news unless i'm in the 50's levels.