Getting high enough DPS to get through the map on Ruthless took me a while, had to farm some of the new patch pets.  All toons need max resistence and good health/dmg stats.  This map on Ruthless is no joke.  Right now I use 3 AFK characters (Summoner, DPS Monk, and Hunter) standing on the egg in a triangle with Auto-fire on (in the directions the egg is gonna move that wave) and 1 active character (Hero Boost Monk).  Make sure 1 of the AFK characters on the egg has your best cat pet.  I also use one of the healer-type pets on an AFK characters (desert goblin or the cupid one).  Put your best pets on everything else.  With the Hero Boost Monk I take the lead and build slow auras and strength-drain aruas along the route as often as they fit.  If your pets are elemental, try to mix-match elements to counter mob resistences.  The strength-drain auras help with this as well. I tend to have the DPS monk use Hero Boost when a wave starts and as his fades, I turn on the Hero Boost Monk's Hero Boost (which is lots higher), to get overlap of heals and ensure hero boost stays "on" all the time.

Harbrengers (spelling???) are freaking cheaters, stay distance from them if possible.  I have not lost to anything else, but if you get double teamed by Harbagers, you drop super fast, especially true on the last wave up to the build spot, so be aware.

Once you get to the end, the build isn't bad, just Hermit stuff and Auras and Buff Beam with some layers of reflective towers and rows of minions between the sets of towers (just holds up the big mobs and keeps them off your stack.  I swap out all charcters at this point to 3 summoners and a Tower Boost Monk.  Tower Boost the whole time which is pretty easy given the incoming mob density.

Loot rolls pretty good, and you get 2 eggs per player (same as Nightmare), so 8 total if you run 4 toons.

Good luck!