The Garden of Death is the seventh multi-player "dungeon," for level 50-55 characters. Teamwork, with everybody doing his job, is critical to defeating the final boss.
You'll want a well-coordinated party for the Garden of Death. Bring at least one mage with a good set of healing skills, and either a 2nd healing mage or an archer who can shoot Freeze arrrows.
You'll encounter two sets of bears in the final stage, just before the boss. Everyone should resist the temptation to use big attacks here. Use the bears to build rage to 100% so you can defeat the final boss. Don't worry; they have a lot of hp but they don't hit hard. You can get through the battle with no healing and no big attacks, without taking much damage at all.
The basic strategy for this boss (and the one in the Badlands) is to stay alive longer than the bad guys. Expending rage on flashy attacks (or flashy heals) will kill you.
Before you attack the final boss, check:
The mages' job is to keep the rest of the party alive. The archer's job is to freeze the enemies so that the mage can keep up.
The mage should open with Suntoria. Resist the temptation to use massive attacks; you'll need your rage for healing.
The archer should shoot Freeze every time it's available. Don't hesitate to use it. Freeze as soon as you can so it can countdown to the next use. Every time you Freeze, you buy time for the mage to rebuild rage and the healing spells to cycle through their countdown. The most common cause of failure in the Garden of Death is when the archer gets carried away and uses big attacks instead of freeze; resist the tempation to show off how strong you are and keep on freezing, and you'll win.
The boss's bleed attack does 4000 hp damage per round, so the mage must have Purification to counter it. The boss's lightning attack causes bleeding. Cast Purification as soon as you see that, or you'll lose.
Blessed Light uses up 60 rage. If you have two mages, it might be useful, but otherwise it can be fatal. You can get a full heal in one round, only to exhaust your rage so it's not there when you really need it.
Knights should use their bubbles to reduce the amount of damage they take.
Everyone should be prepared to use healing runes, and use the first one early so that it will have time to countdown. The second most common cause of failure in the Garden of Death is when the knights or archer put off using their healing runes, so that the mage falls behind trying to keep them alive.
In addition to keeping Suntoria going and using Purification to counter bleeding, the mage should cast Restore (individual heal) every time it's available. Don't hesitate to cast Restore; cast it early and often so that it can cycle through its countdown and be available again.
Halfway through, the boss will summon minions. One minion has weak mdef, and the other has weak pdef.
Don't get discouraged. If everyone does his job correctly, you'll win!
The Nightmare version of the Garden of Death is probably the most popular place to pick up Legendary Stones. You get level 50 stones here, and fully enchaned level 50 legendary equipment is more of a power boost than normal level 60 stuff. You'll get a stone from each of the two sub-bosses, but the Summoner is the major source of Legendary Stones.
Game play is identical, except that the beasties have twice as many hp and hit twice as hard. Strong level 60 players should be able to get by.
We skip the optional side trips in Garden Nightmare; no Legendary Stones to be found there. Your first goal is to get past the two minibosses.
The Summoner is just before the big boss, after you've defeated the Snuggle Bears. (Their bear hugs are a little rougher, but still no problem. Build Rage.)
The Summoner will want 5 skeleton keys per run, so make sure each member of your party of four has at least 25 keys before you enter the dungeon. She will summon the Soul of Borno, who when attacked summons identical copies of your party's characters for you to fight.
Before you attack, have everyone in your party remove all defense gear. Take off anything that gives you HP or any kind of defense. Don't forget to take off defensive astrals and clothing items, and dismount your hourse. Where you have the option, equip skills that give your mirror selves stupid things to do. Mages should have Purify equipped and Archers can equip Scattershot; really silly to use in this battle so you can hope your mirror self will waste turns by using these skills. This gives you a tremendous advantage over your mirror selves. You already have rage. They will start from zero. So open with AOE attacks and defeat them quickly before they can build rage.
You might run out of hp packs while battling your mirror selves. If so, just let it go; don't equip more hp packs until you're all done with the Summoner. That way, your mirror self will go down with the first AOE attack.
You can do 20 runs with the Summoner on each visit. Don't waste them. Before you enter the dungeon, make sure that everyone in your party agrees that you will do all 20 attempts.
Each battle from the Summoner will get you 1 or 2 level 50 legendary stones so you should come out with 22 or more stones per run through the garden.
Each piece of equipment requires 100 Legendary Stones to synthesize a Legendary version of the item, so it will take 4 or 5 runs for each of the 8 pieces.