Thanks to EspioKaos for his prompt translation!
According to what appears to be a scan from Famitsu (possibly Famitsu Connect!On?) that was anonymously uploaded to PSO2uploader, Dark Falz will be encounter-able in an emergency quest which may be added some time in December.
Falz itself is planet-sized (well more like the size of a moon), so players will not be fighting him in the same way as they did in previous Phantasy Stars.
The gist of the emergency quest is that Dark Falz attacks an Arks Ship. Players will have to fight against multiple Falz Arms and if enough of them are defeated within the time limit of the quest you’ll be able to go up against its body, named Dark Falz Elder.
Guess that neatly solves the mystery of “dpfisharm” and “dpfishelder”. Not quite as fish-like as his Phantasy Star Universe incarnation…
At current, there is no more information than this. However, we should be due a new update page soon so hopefully more will be explained. Unless this is for the second half of December of course.