I tried this in the T15 tier because I was sure I would zerg him in the last phase. However the tentacles in Phase 2 were really hard to kill since only Unleash Elements (15s CD) would damage them while gripped. Apparently the legendary cloak proc can also damage them so I guess I lucked out big time. Besides holding UE for the tentacle grip I used EM+PE default PVE build for the final phase burst.

The MMO-C Shaman Solo Thread:
http://www.mmo-champion.com/threads/1238851-Shaman-Raid-Boss-Solo-thread-(Panda-edition)

My Armory:
http://eu.battle.net/wow/en/character/aggra-portugues/Zephyr/advanced

Songs:
Ulduar Interior Yogg-Saron
YGO-GX Supreme King Theme
BABYMETAL - Catch me if you can