Quote: "Can we include combat?"
Yes, but simply killing enemy A and B so a door opens is not really considered a puzzle.
Quote: "I have a gun in my level. Though there will be no enemies. Am I able to do this or no?"
Yep
Quote: "Now when you say puzzles can we make obstacle courses like platform jumping and stuff like that?"
You can include those if you wish but again that's not really a puzzle, more a test of skill.
Quote: "Are shaders allowed?"
No mods or external "enchantment" files. So 3rd party shaders not allowed.
Quote: "What is the gore limit would you say? I.e., how far are we allowed to go gore-wise?"
Being as this a puzzle competition, there's no need for excessive gore. Remember all entries will be able to be downloaded by anyone here. Bond's Chainsaw Brute would be considered excessive gore.