here is a pic of my Duncan, I haven't had it very long so I cant say anything about its growth yet, but it likes moderate to light water flow and medium to high lighting. I target feed mine brine shrimp every two to three days and it is so far, thriving.
Its rather interesting that this still seems to be a coral that has not had a huge amount written about it and in some parts of the world is considered a rarity.
Info taken from:
Eric Bourneman - Corals, selection, husbandry and natural selection
Its natural location muddy substrates or shadowy locations in tubid waters
Colours are normally green, blue-gray or brownish
Care in our tanks: Apparently hardy, (however I have read numerous posts to the contrary) and adaptive to most light conditions. Require gentle flow. Duncans contain zooxanthellae but require feeding for maximum health and growth.
Where are they found: Australia, Papua New Guinea and indonesia
Shelaghfishface, down the bottom of that last picture you posted there are some very small bright green zoa looking polyps?
I have some of those that came with my live rock and I have no idea what they are or what they require, do you know what they are?
Once established, the polyps really extend a good 3-4 inches. I feed it mysis and enriched brine twice a week. Sometimes i'll chop up uncooked shrimp to give it as well.
One thing to add is they are very temperamental and sometimes will close up or look sickly for a few days at a time. Most often, waiting it out is all that is needed to get the coral back to new (assuming your params are all good)