Gotham is a weird show when it comes to the cast — it's so big and constantly shifting that it's hard to tell when someone has left for a while and returned. It seems that once you're part of the show you stick around, appearing every few months just to keep things fresh. That is, until they kill your character — though that's no guarantee you won't be back. The closest thing there was to a clear cut return of a character has to be Jonathan Crane, aka the Scarecrow — and that is a bit of a twist there too.
The character of Jonathan Crane (Charlie Tahan) first appeared in a two-part story in season 1 where we met him and his father Dr. Gerald Crane (Julian Sands). We saw all the beginnings of the Scarecrow in his father with the fear gas and the experimenting on people. Jonathan ends up being hit by the gas and driven insane, leaving him in Arkham Asylum.
He is then put aside until the beginning of this season, when a gang looking to bring down the Penguin (Robin Lord Taylor) busts Crane out to get control of his father's fear gas. We see just how crazy Crane is as he takes on the guise of the Scarecrow. This is a major departure from the comic version of the character that is the doctor who creates the formula. The Gotham version is basically split into two.
Then the character went away again for a while only to resurface to work with Jerome (Cameron Monaghan) and Jervis Tetch (Benedict Samuel) in the plan to drive all of Gotham City crazy. The interesting thing is that a different actor was playing the Scarecrow. David W. Thompson replaced Tahan, but he's never shown without the mask and there was no reason given for the change of actor. The show has made changes before, recasting the role of Ivy Pepper / Poison Ivy twice, going from Clare Foley to Maggie Geha to most recently Peyton List, but each change came with an event in the series that explained it. Nothing for the change of Scarecrows. How that will work out over the shortened finale season will be interesting to see.