Hello, can I use assets from marketplace demo, for example ice rocks from Elemental for my own commercial project?
Yes you are allowed to use them: https://answers.unrealengine.com/questions/26453/unreal-engine-stuff.html
"Also, you can use all of the free Epic content in the marketplace commercially in any games you build with UE4. This includes all of the content residing in example projects. For example, all of the weapons, meshes, sounds and materials in Shooter Game. Tappy Chicken even! A new, community-hosted Unreal Engine Wiki - Announcements - Unreal Engine Forums hope that helps "
wow! amazing, thanks!