This is how Post Credits: Thunderwing plots revenge goes in Crash's, Thomas' and Ryan's Adventures of LEGO Dimensions.
[We see Thunderwing walking with his body damaged]
Thunderwing: That Ryan ruins EVERYTHING! If only I could go back in time and prevent him from being created!
[Thunderwing smashes a rock that lets out a purple glow]
Thunderwing: What's this?
Ryvine Sparkle: What's that?
[Thunderwing unearths the object from the rock, revealing it to be the Dark Spark]
Thunderwing: Ah, the Dark Spark. With this, I will go back in time and bring the war to Equestria so it can continue endlessly again.
Ryvine Sparkle: Mind if I put it in storage just in case? This Kingdom Hearts is connected to the Keyblade war.
[Thunderwing nods and the film ends with Ryvine putting the Dark Spark into storage]