From Dota 2 Wiki
Challenges are quests exclusive to Dota Plus subscribers. Each hero has its own set of challenges, which can be completed to earn hero levels.
- Completing a challenge earns experience points towards a hero's level.
- Three challenges are available at a time.
- Each challenge has three difficulty tiers that reward increasing amounts of experience.
- Challenges can only be completed if the match is won.
- Challenges can be refreshed once every two weeks.
- Challenge progress is not cumulative through multiple matches unless specified.