I know that this jam is not horror only, as it can be hallowen themed without horror, but I want to ask about the horror and what we can and can't do about some common things in horror games, like can the game have blood, psycological themes, gore, body harmfull alteration (like losing limbs, or adding limbs), suicide? I ask this because in the rules we have "...and many of our participants and audience are minors in their location." and "...or statement of intent of suicide or self-harm are similarly disqualified...", So I want to know if I can add x or y to the game, what can I show as image but cant show in text or audio (and what can I show in text but not as image, etc...), what the limit of x and y.

Blood, and psychological themes are generally fine.

Gore and disfigurement is permitted but as a judge I recommend it in moderation if you are competing for ranked prizes.

You cannot demonstrate/instruct, glorify, or issue a statement of intent of suicide,. You've omitted in your quotes.  There are a few exceptions to this, such as instances of noble sacrifice where the desired outcome isn't strictly self-destruction.  As the host of the jam, I would recommend staying far away from suicide as a type of content, as your entry can be pulled, ranked or not, if any of the judges feels it violates that rule.  Visually depicting the act of suicide, or the immediate aftermath of one always violates the rule.