To find Ishteen the player must have spoken to the "Huntmaster" in Phon Coast and defeated Thalassinon, which will trigger the start of the Rare Game quest.
Ishteen then appears within the Barheim Passage in The Zeviah Span and East-West Bypass. Its odds of appearing in these two areas increases by 2% every ten seconds the party spends there. The odds will hit 100% after roughly eight and a half minutes. It will appear right next to the party.
Like all Trophy Game it will never respawn once killed. It is actually possible to zone back and forth between the two zones, and make it appear in both, stealing one Soul of Thamasa from each.
Ishteen is not particularly a tough enemy to defeat. It knows many high level spells and can use Death to instantly kill a party member. It can also use Doom on a party member. Like the Rare Game Negalmuur, Ishteen knows the ability Necromancy.
Using this ability, it summons the undead (in this case, Dead Bones). Unlike Negalmuur, Ishteen does not use Necromancy frequently, so the auto-Leveling trick is not good to use on this enemy.