Hello!
So, this has come up before, but in a post with a couple of different problems, and this one never got answered.
Basically: When using FollowCharacter on a scrolling background, the following character gains an unsightly graphical glitch where the sprite twitches and flickers as the room scrolls.
I've played around with various variables and found some that seem to mitigate it a little, but it's always still there. Any tips on how to get this looking smooth would be enormously appreciated.
Try the Smooth Scrolling module (http://www.adventuregamestudio.co.uk/yabb/index.php?topic=33142.0).
It decouples the viewport from the player's position and there's a good chance it'll fix the issue.
You continue to be a legend.