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This is a fine line to summarize the suggestions in this post, because I have scattered them around and not bothered to suggest them altogether. Let it begin!:
1. Antimatter slider to a planet because evaporating planets, stars & anti-planets, anti-stars are fun
2. Creating an exotic planet would require you to put a minus sign in front of the mass which means the object would repel all but negative mass (Also known as anti-gravity).
3. Evaporating black holes, meaning they would shrink and go poof out of existence.
4. White holes would be the negative of Black holes where light would bend and repel and only eat exotic matter objects.
5. Just a small thing, L Brown dwarves (planets 88-104 Jupiter mass), T Brown dwarves (planets 87-58 Jupiter mass) and Y brown dwarves (planets 57-wherever gas giants start to naturally heat up, Jupiter mass).
6. If dark matter exists, then the milky way shouldn't rip apart and maybe use it as a way to increase the gravity range on an object so orbits don't go haywire.
7. Finally, the shock waves could echo through space, for example: planetary collisions, supernovae, planet explosions...
That is all I have.