Valve removed Warlock from the hero selection in any mode of Dota 2. The reason is the bug that allowed the players to get a massive XP boost early in the game. The description of the glitch was released on Dota Today Telegram channel.
There are multiple versions of the execution of this bug. They all required putting Black Grimoire for sale, then moving it back to the main inventory and delivering it to the stash. At some point, Black Grimoire becomes infinite when used from the stash. Through these shenanigans, Warlock's level could've been maxed out at around minute 10.
There was another glitch of a similar nature with Witch Doctor, and Gris Gris. Both bugs were reported on Valve's official tracker, but only Warlock was removed from matchmaking.
There was another hero last year who was temporarily disabled from Dota 2. In July 2024, Valve was fighting against multiple Meepo bugs. After some initial fixes, they moved the character to the inactive pool. It took less than 24 hours to bring him back.