Just did this in ulduar right now, if u are on ur first go thru the trash. you can range pull the stuff at the door where leviathan comes out and run back behind where his wall pops up and he will attempt to go thru the wall and reset, then a new set of vehicles will spawn and u will have twice the amount of vehicles available to you.
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Sry, forgot to SS, but u basically engage him from ranged with the cannons on the demolishers, and run back out of the force field area before he puts it up, he will evade when trying to go through it, reset, and new vehicles will spawn.
We had somebody accidentally do this our first night in Ulduar, and while a second set of vehicles did spawn, we were also stuck in combat until we exited our first set of vehicles and allowed them to despawn.
Can confirm this one too. Though my guild was stuck in combat for 3½! hours so had to run out to do food buffs and such - also mount up and run after each wipe >,< was a frigg*n pain in the a*s
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