Yes, you can see Epcot and the mountain rides easy
Blizzard Beach and Volcano Bay are both fantastically fun places to go during Summer time. Yes, absolutely one can see just about everything the higher up you go. I especially love all the high rides. You can see everything.
Yes you can
I have not been to the top of the volcano but I'm pretty sure you could see the Universal Hotels and possibly some of the rides at Universal Islands of Adventure like doctor Doom's and the Hulk.
Nothing Disney or Universal related is visible.
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