We were definitely killing the zombies one at a time, easily 7-12 meats spawned almost immediately, which were negated by Divine Guidance after which they immediately wiped the group. When we wiped once from it, there were easily at least ten "A Piece of Necrotic Flesh has been reset" that spammed the chat log, so either there's two immediate spawns of five or the numbers are bigger then expected.
Also, it bears mentioning that a good amount of "optional" fights in this are substantially harder then the boss fights proper with zero reward to speak of. The copy swarm is an almost guaranteed pug killer until there's people with better gear and even then, the damage is higher then virtually every single boss except for the Vampires/Zombie boss (and it's still less), and despite all that you get zero loot and just a quest update for it. The first time we aggroed it, the auto attacks alone were all aoe and basically instakilled the group, with the tank dying afterwards. The four or five AA gains is really nice, but it kinda makes for sour grapes when you spend a while getting demolished by trash if you don't have it coming. It really feels like they're way overtuned for some odd reason, though that could just be me speaking as a pug. The drolvarg swarm was also a bit of a "What the heck?!" moment when all the drolvarg spawned, were immune to aoe, then proceeded to devour the healer/squishies.
I just remembered, if you reengage the drolvarg after the fight, they do not count as an encounter. Dunno if this was intended or not.
One more thing to mention is that an enchanter absolutely trivializes this zone, at least in terms of two or three encounters. This is in no way bad, just something I wanted to make mention. The first boss, the swarm trash, and the vampire boss can all be aoe mezzed/locked down, so they get utterly stomped by any group with a chanter. Alternatively, an extremely high geared tank/healer combo or two healers/one tank seem about right. It definitely feels like ToFS thus far is "Bring an enchanter, or else," which is great since it requires more intelligent gameplay but is kinda painful when you get a bad chanter/there's not many around. Great instance though.