This page is just a reference of all the known Steam APIs, I do not know how they work. Please do not email me with questions.
UNDOCUMENTEDGetLeagueData
https://api.steampowered.com/IDOTA2League_2305270/GetLeagueData/v1/
UNDOCUMENTEDGetLeagueInfoList
https://api.steampowered.com/IDOTA2League_2305270/GetLeagueInfoList/v1/
UNDOCUMENTEDGetLeagueNodeResults
https://api.steampowered.com/IDOTA2League_2305270/GetLeagueNodeResults/v1/
UNDOCUMENTEDGetLeaguesData
https://api.steampowered.com/IDOTA2League_2305270/GetLeaguesData/v1/
UNDOCUMENTEDGetLiveGames
https://api.steampowered.com/IDOTA2League_2305270/GetLiveGames/v1/
UNDOCUMENTEDGetMessages
https://api.steampowered.com/IDOTA2League_2305270/GetMessages/v1/
UNDOCUMENTEDGetPredictionResults
https://api.steampowered.com/IDOTA2League_2305270/GetPredictionResults/v1/
UNDOCUMENTEDGetPredictions
https://api.steampowered.com/IDOTA2League_2305270/GetPredictions/v1/
UNDOCUMENTEDGetPrizePool
https://api.steampowered.com/IDOTA2League_2305270/GetPrizePool/v1/