UnderFoot Progression

Progression in Underfoot is fairly straightforward. Originally you are limited to just Brell's Arena, Tier 6, and Tier 7 zones. To move beyond this into the Tier 8 zones you must appease The Gatekeeper located in Brell's Rest. At any point you can say "enter" to him to get a message telling you the next zone you need complete and who to talk to. You can complete the requirements out of order, he will simply tell you the "easiest" zone uncompleted. The steps are:

Brell's Rest - Don't Fear the Destroyer
Cooling Chamber - Tasnise Underbelly
Pellucid Grotto - The Seeding Frenzy
Foundation - The Search for Saunk
Underquarry - Scent of a Woman
Arthicrex - To Serve Sporali

Each of the above is an instanced mission with their own task requirements for requesting, however for progression you need simply attend and complete the missions provided at least one person can get it. After completing all 6 zones' mission or raids you will be able to use the teleport pads to enter the Tier 8 zones. Additionally you can do all the tier 6 raids, but it is not known yet if you can mix and match, ie if you do BR raid but all other zone's missions will that count.

Once in Tier 8 you will again need to complete each zone in order to move forward. This means completion of the following missions:

Kernagir - The Silent Schism
Fungal Forest - The Fungal Bloom
Lichen Creep - Bonfire of the Adherents
Brell's Temple - Fire In The Hole

Again, each mission has requirements for requesting, but only participation in winning the missions is required to become flagged. You can alternatly complete the Fungal Forest, Lichen Creep, and Brell Temple raids to be flagged. Completition unlocks the first of the Tier 9 zones, Volska's Husk. Access to the final zone in April is of course unknown, though it is assumed you will need to complete the Volska's Husk mission

Kill the Greken Hatchlings.