Disclaimer I have not played Terraria on the PS3, so this answer is not first hand.
If you can beat the Twins and Skeletron Prime you should not have much of a problem with Ocram, assuming you put some time into crafting weapons/armor from the best available tier.
LevelSave - The Toughest Bosses In Terraria claims that he is actually easier than both The Twins and Skeletron prime when you its possible to fight him. Ocram is #4 on his list. The Twins and Skeletron prime are #3 and #1 respectively.
While compiling my list there were many factors that came into
consideration. Should all the bosses be considered on the same scale?
Should they be considered equal on all fronts? In my mind that isn’t a
fair way to rank them, while one is playing in normal mode the gear
and weapons are clearly inferior to those available in hard mode. That
being said I decided to consider the bosses in the time that a player
would first face them.
Some more anecdotal evidence:
A post on the Terraria forums
Masamune1004 write:
I can defeat him by standing in one place holding R1 and aiming up
with a harp in full hallowed armor, with heart statues but without
using meteorite/hellstone. Usually no potions either, sometimes one
greater health potion if the servants don't feel like dropping hearts.
So basically he can be defeated afk (or afc in this case :p).
It isn't easy to tell if the biome you are in is surface or not because of the walls behind the house, I suggest breaking all of that. Also, as it states in the wiki, "to get the Truffle to move in, there must be housing in a surface Mushroom Biome during hardmode." judging by the list you have provided you have done all of the things that are required. All that's left is to see if the house you built is even suitable for NPC's.
As it states under the NPC section of the wiki, a suitable housing has:
- Proper Lighting
- Enclosed frame composed of blocks, a door, and walls. (Size: About 5x12 blocks)
- 1 Flat Surface Item (Ex: Table, Dresser, Bathtub, Bookcase, Workbench, Piano)
- 1 Comfort Item (Ex: Chair, Throne, Bench, Sofa, Bed)
From the pictures you gave, the program might be mistaking your Surface biome as an underground one because of the excess grass walls or not enough lighting. Another thing might be the height of the room.
If nothing works, just have a little patience, NPC's sometimes take a while to move in. Also, just try to preoccupy yourself with something else while waiting to help pass the time. Another thing, those walls inside the house must be player placed, if they spawned that way (Which I doubt, but doesn't hurt to inform you) you need to remove them.
Please Note: that there is a bug where if you killed the boss Plantera before the Truffle moving in, he will not move in and you will need to make a new world
Best Answer
The depth the underground starts at depends on the size of your world. The easiest way to make sure you are in the underground is to have a Depth Meter (or one of the accessories made from a Depth Meter) equipped. Its status display should list "Underground" as your location.
In general, you need at least 200 blocks from the specified biome for the game to treat that area as that biome type, but some biomes have different requirements. The Terraria wiki has a complete list of what is necessary to create each biome.