In a bizarre turn of events, Valve added a whole fighting game to DotA 2. Not as some sort of custom mode that DotA is known for, but as a mini-game for its Crownfall event.
The recently unlocked Act III almost immediately opens up with the "Sleet Fighter" tavern brawl, where you take control of Tusk in his fight against Bristleback. After that, you can enjoy the mode on its own as one of 5 different characters, with each having their own unique movesets.
It's obviously not as complete or intricate as full-fledged fighting games, but it's amazing that it exists, and they even added local, multiplayer!