look at the guide park map when you enter a park.
it will list the times and locations for a meet and greet period.
at ioa, the fabulous 4 make an entrance on atv periodically during the day.
UO has photographers to take your pics with the live characters.
you will find spiderman at the shop on the corner to the ride daily.
the scheduled meets are always listed in the park map.
in each section, you will find characters that are themed to that area.
the characters change frequently so i can't tell you which ones you will see when you are there.
at the studios side, besides the costumed characters as mentioned above, you will see look alike characters.
last week i saw ricky ricardo driving a convertible with lucy and her trademark polka dotted dress and umbrella, driving around the streets there.
marilyn was there in her trademark white halter dress posing with guests for pictures.
many people were out for photo shoots with the park guests.