Here are some tips on how to beat the level 58 death boss. I managed to do it on something like my 6th try without any henchmen or treasure cards.
Load up your decks with as many Death Prisms as you can. I didn't do this, but you could put in a Reshuffle or 2. If you don't want to spend the training point get the Amulet of Disorder, it gives one Reshuffle card. Don't put in Animate. The minion will use up your prisms and cause more harm than help. Kill the minion first using only 1 death prism. Get the max number of Death Blades, Death Traps, Curses, and Spirit Blades. Get 2 or 3 Feints and Spirit Traps. If you don't have Spirit Blade and Spirit Trap already you'll want to get them. Don't worry about the Curses the boss places on you, he'll eventually put on more then he'll use, and it's only +20%. Don't wear the Level 58 armor because it gives no death resist. You can put in some Death Shields if you want. Get the max number of Wraiths. You can put in the sun school accuracy boosters if you would like to. If you want to use Scarecrow only have 1 or 2 because the minion is easy to kill.
Use loads of buffs. You mostly likely can only hold 5 or 6 Death Prisms. The boss has 13,300 health so you'll want to do as much damage per prism as you can, especially if you don't have Reshuffle. Before each Wraith on the boss make sure you have at least a Death Blade, Death Trap, and Spirit Blade, though I highly suggest you have more. If you do that your health will probably not be an issue.
Keep trying if you don't beat it at first, Skeletal Dragon is worth it.
Feel free to post guides on the other level 58 quests.
It really helps to have the feint amulet, too. This puts a 75% trap on the boss and a 20% trap on yourself. Use a death shield when he is about to throw a strong hit, and DEFINITELY wear clothing with at least 20% death resist. Here is what I suggest doing:
1. Mark your spot inside the tower. 2. Kill the minion first; you only need a few cards for this. 3. Flee and port back, mark your spot again; the minion won't be there when you come back. 4. Make sure you go first. If you don't, just flee and port back again, mark your spot.
I killed him in one hit: spirit trap, prism, death trap, feint, feint amulet, deathblade, spirit blade, treasure death trap and curse = 18,270 wraith :-) My death boost was about 30%, too.