Promote:

- New mechanic
- Coding problems based on NP problems. This makes solution that are easy to implement inefficient and solutions that are hard to implement efficent. (eg. Stanek)
- inter-mechanic synergy
- Simplicity (eg. Stanek, Hashnet. bad example: Corp)

Avoid:

- Failure conditions, it's very frustrating to revert several days worth of progress.
- Making existing mechanic harder. This makes it hard to port the content to other BNs.