Hello again!
- Chest is empty now, but we fixed it in upcoming update. And no, water form is not here ) You can find it during your journey.
- Are you using mouse + keyboard input? If so green slime can be picked with south-east direction (down + right arrows or S+D) while radial menu opened.
- The concept of the game implies that not only world can be discovered by player but forms and their possibilities as well. So you should try different ways to apply new abilities and discover their features. But looks like additional tips are required.