Challenge variety

1. Game Difficulty vs Player Difficulty (Gamification Player Progression Tips)
2. Gameplay Difficulty vs Player Skill Level (Gamification Player Progression Tips)
3. Experience Gain vs Skill Gain (Gamification Player Progression Tips)
4. Player Achievement vs Player Advancement (Gamification Player Progression Tips)
5. Skill-Based Progression vs Level-Based Progression (Gamification Player Progression Tips)