Style Transfer. This is a case of cartoon characters swapping Artstyles AND animation styles.

1.

At first, They glow their main colors.

2. 

Then they transform. But they scream in pain during it, due to the style transfer being EXTREMELY PAINFUL for them.

3. 

They are a bit rag-dolled to the floor for a moment, then they show their changed forms. which they can change back, which is still VERY VERY PAINFUL FOR THEM.