Earlier this week, a bug was discovered where Monkey king could only transform into Bounty Runes at the old rune spots and not the new ones. While many laughed it off, few would have expected an even more drastic bug.
Yesterday, it was discovered that Monkey King could transform into Roshan with his mischief ability making for more hilarity.
All you have to do is kill Roshan, pick up the items and then click the Mischief ability in the pit to transform into Roshan
Unfortunately, this is largely just a cosmetic buff and you get no real advantage in the game.
However, there is perhaps one use for this. After killing Roshan, Monkey King can move into the pit right before he spawns transform into Roshan and maybe hope to bait the enemy team into the fighting him.