I thought of an interesting idea that would make the random mobs little more interesting than just random encounters. Imagine that when you went to a lava planet, the creatures there had fire effects and could cause you to burn. Jungle planets having poisonous creatures on it. Grasslands having just strong creatures without necessarily having any element. Ice planets giving creatures the ability to frostburn you, I think you get the picture. I could see this as going really well. When I say to have the elements assigned to planets though, I would assume that you'd still be able to encounter other elements, just not as much. I can imagine this as being very fun because I would see the player as landing over an ice planet, bundling up in their warmest clothes, and preparing themselves for the elements accordingly. It would add an interesting layer of tactics that I would love to see!