NPC #42098 (possibly named "Invisible Stalker Cataclysm Boss Ignore Combat Floating") doesn't exist. It may have been removed from the game.
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Invisible Stalker (Cataclysm Boss, Ignore Combat, Floating) - Live
Invisible Stalker (Cataclysm Boss, Ignore Combat, Floating) - PTR
Invisible Stalker (Cataclysm Boss, Ignore Combat, Floating) - PTR 2
Invisible Stalker (Cataclysm Boss, Ignore Combat, Floating) - Beta
Invisible Stalker (Cataclysm Boss, Ignore Combat, Floating) - Cataclysm