[quote=@The Fair Lady]
Ello. I don't know if you remember me but I was in the last version. I played Nihris lastborn, and was the creator of Lymaeus too. I was hoping to use Nihris again but there is already a god who does the ferrying between this world and the underworld. Can I still use her?
[/quote]

Things that come to mind if you still want something associated with the underworld -

God of Tartarus? Imprisonment and isolation maybe? you could be the one in charge of keeping all the big nasties from getting out of Tartarus. 

Alternatively you could be our version of Thanatos, essentially the Grim Reaper, the personification of death. We have a Charon and a Hades. Someone to take souls to Hell and one to lord over them there, but we could use someone who turns people from mortal to soul ;D

You could make the god of judgment? The three judges of the underworld, Radamanthus, Minos and Aeacus could all be one deity perhaps? so you judge the souls that come into the underworld maybe? 

Or the Fates? getting further away from Hades now, but the three women who decide fate? One to weave the string, one to judge the length of the string, one to cut it etc etc.