Howl O Scream is it's own ticket. And yes a majority of the rides are open.
Think Howl o Scream started at 6 last year and everyone had to be out so people for howl o scream could get in. And it might be like a normal day minus the quick pass not really sure
The Hallo Scream thing is only for the evening, didn't include the daytime admission. But I believe everything will be all inclusive while there.
typically busch gardens admission tickets are for everything. you don't have to pay separate for park rides.
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