One way to make a dice "tricky" is to have it show lower numbers more often than it would normally. A few ideas:
- Every other time you roll a 6, turn it into a 3
- If you roll a number greater than 3, subtract 3 from it
- Divide your roll by 2 or 3, and return that number
- Mod your roll by 3 or 4 and return that
- Use two random numbers to decide what you should return