When you've made it to the crypt you've finally found Gudar's Ghost. He's pretty tough but at the levels my characters were at when I tried this, I beat him rather easily. The important thing to do is to have Random and Coryool do their magical attacks, have Sarah use Nympha Para, and have Luciana cast Protection until everyone stops responding. You can save your game at the save point before you fight Gudar's Ghost just in case. After you defeat him, you can get to all of the treasure, and there is a lot of it. Once you've defeated Gudar's Ghost, you can egress out of the Manor and go on to something else, unless you haven't gotten all of the items in the manor.
Location A: There is a Yveen Save Point
here.
Location B: This is Gudar's Ghost.
Location C: Hidden in this tomb are 1000 gp and Gudar's
Spear.
Location D: Hidden in this tomb are 2 Saphirs, 1 Emerald,
3 Mithrils, and 2 Diamonds.
Location E: Hidden in this tomb are 2110 gp, an Orb of
Wisdom, and "The 4 Saviors", which teaches the spell G-Wave.
Location F: This is Gudar's friend, and if you talk to him
he will give you the RuthGarden Key.
Location G: Hidden in this tomb are a Dark Amulet, a
Cryzalis, and 12000 gp.
Location H: This stairway leads back up to the Main Area,
Location L.