The Storm King's Vengeance - and how to complete the quest

I found a way to kill Algar the Chosen without being mounted on Gymer.
1) Mount Gymer and go to the Reliquary of Pain
2) Once there walk into the portal that teleports you to the floating building above.
3) You will notice that once you get teleported up there you will be stuck. Simply log out and log back in.
4) The game will now think that you are still mounted on Gymer and therefore put you in the phase where you can see Algar the Chosen.
5) Fly back down, pull Algar in the air and kill him (you might need help soloing him)
Please be aware that i did this on Ragnaros, so it might not be possible on Lordaeron.
-Hope this helped and good luck!

How I did this quest on Lordaeron.

1. Kill everything, except Algar the Chosen while riding Gymer
2. Go to Algar the Chosen
3. Leave vechile (Gymer)
4. Kill Algar the Chosen

Don't know why everyone dismounts Gymer. I killed everyone and completed this quest and still had 150K+ hp on Gymer.