1 why do we need to make up an scp,

2 can we just make  up an scp and not use scp sandbox

3 can we use existing scp for details e.g the  tickle monster roaming around

1. Yes. You can publish if you want or just keep it to the game. 

2. Sure. Your imagination is the limit. 

3. Yes, you can even use SCP 682 if you want and add Dr. Bright as well