While watching Dungeon Train, I noticed Finn attacking everything that looked evil or whatever would drop loot.

S5 e36 Finn jumping over a rock monster
He was very destructive and just acted on the voice in his head.

When watching Vault of Bones though, he thinks his moves out more clearly. He wants to make sure he doesn't destroy any loot or kill anyone that doesnt need to be killed.

Flame Princess started to attack everything that looked evil and burned whatever she could, revealing her chaotic side.

Flame p
Being destructive cleared their minds. FP was greatful to be able to destroy stuff again and Finn loves a good dungeon crawl. (Well, dungeon ride.)

I just thought they are both naive and playful. FP has matured from the last time we saw her and Finn is starting to put himself back together.