Good catch with Trine, played the first 2 a long time ago and might be the inspiration subconsciously but forgot about the series.
Definitely would have been something similar, in the original idea you could not "finish" the game with only one character because some collectibles would be hidden behind obstacles only 1-2 characters could access so you needed to switch monsters, and the peasants where meant to be an Easter egg not the starting characters ... oh well.