Planes of Power flagging guide

Checklist
Plane of Innovation Plane of Valor Plane of Storms Crypt of Decay Plane of Tactics Halls of Honor Bastion of Thunder Plane of Torment Solusek Ro's Tower (requires Marr, Saryn, Tallon, Vallon, Bertox)
 * Kill Manaetic Behemoth (flag for tactics)
 * Kill Aerin`Dar (flag for HoHonor)
 * Do Askr's quest for access to BoThunder
 * Kill High Priest - get flag to Bertox area
 * Kill Bertoxxolous
 * Kill Tallon and Vallon Zek (partial flags for Solusek)
 * Kill Rallos Zek (partial flag for Elemental)
 * Complete the three trials to gain access to HoHonorB
 * Kill Mithaniel Marr (partial flag for Solusek/Elemental)
 * Kill Agnarr and hail Karana (partial flag for Elemental)
 * Kill Mareeq and free Tylis in his event
 * Kill Saryn (partial flag for Solusek/Elemental)
 * Kill 5 mini-bosses
 * Kill Solusek Ro (requires Rallos Zek flag)

(All Elementals require Marr, Agnarr, Saryn, Rallos, and Bertox. In addition, PoFire requires Solusek) Plane of Earth Plane of Air Plane of Water Plane of Fire Plane of Time
 * Kill Mystical Arbitor to gain access to PoEarthB
 * Kill the Rathe
 * Kill Avatars to gain access to Xegony.
 * Kill Xegony
 * Kill Coirnav
 * Kill Fennin Ro
 * Create (or obtain) odylic vial
 * Combine four elemental parts to create the Quintessence of Elements.
 * Hail Maelin in the Library
 * Enter Plane of Time via Plane of Innovation

If you're stuck and need to get help to figure out what flags or steps you're missing, check out this Planes of Power log checking tool