My daughter is a huge Loki fan, huge Spiderman fan, and a huge Marvel fan. Loki asked her name on Monday when she met him, and he remembered her by name both Tuesday and Wednesday. He was meeting fans and saw her walk by and yelled HELLLOOO to her her by name. It made her day that he knew her name. She wanted to see him and say hello to him every day for three days. He really made her trip. One day she spotted him wandering around with, or near, Dr. Strange, and she had to go by Dr. Strange to get to him- poor Dr. Strange thought she was coming to see him and he stopped to greet her and she barged right by him to get to Loki! (In her defense, she had at least already taken pictures with Dr. Strange the day before). Loki really is fantastic. So witty and funny!
We spent a lot of time in the Marvel area and at least a few weeks ago:
Captain America had a designated spot and met most of the afternoon every day
Spiderman has a designated spot across from Captain American and meets longer than any of the other characters every day- from early afternoon and he is the last one out in the evening
Thor and Gamora meet together just to the side of the stage (right if you are facing the state) with a designated spot and were out every day. I don't think they were on the app, but they were there every afternoon. Their line will get cut off, so don't wait too late.
Black Panther and Black Widow were meeting together inside a building near the Monster's Inc ride (by where Olaf used to meet if you knew where that is) every day - Dora Milaje-Wakanda warriors escort them out for their sets and at least while we were there stood by at the entrance and exit- if you ask nice they will allow you to take a photo with them. They have the longest lines-- their sets are listed on the app- if you want to see them, try to get there 10 or 15 minutes before they come out for a set.
Groot (full size not baby) meets by the GOTG ride every day even though he was not on the app.
Gamora and Starlord host a dance party several times a day which can be fun to watch. Starlord does not meet.
Loki and Dr. Strange are roaming characters-- Loki likes to go pester Thor at his meet and greet, and is also known to pester Spiderman and some of the other Avengers--- he is very fun to watch. They do not show up on the app.
Those are all I can remember seeing.
The GOTG ride is great-- even if you are a ride chicken, it is worth walking through and taking the chicken exit for a Marvel fan.