If the Nephalem is in Adventure Mode, they may be requested to take down Bashiok as part of Act II's Bounties. This is probably the best way to obtain the Bashanishu achievement, as otherwise, the only way to find Bashiok is to clear the Dahlgur Oasis, and his rarity may lead to players looking for a long time and still never find him.
Named for the Diablo III community manager, Bashiok, the ingame monster appears as a Fallen Shaman (conjurer). It is speculated as a relationship to Bashiok's forum avatar, which is also a Fallen Shaman.
In combat, Bashiok spawns with two random affixes fit for his current level. Note: Some of these modifiers are more commonly seen than others, and various pairings of skills has been reported.