Vikings valued close combat first and foremost, so i doubt they would put efforts on heavy long ranged engineering.
If anything, i'd figure battering rams or heavy stairs against the wall (LoTR style?) were more the Viking course of action...
If you have any kind of aerial troop transport that could work... I remember a winged monster in the Lone Wolf game setting used exactly for the purpose of transporting troops. I have the d20 version book laying around somewhere, i can look it up...
Otherwise... breach the walls in other places. The druid can't have that many Walls of Thorns prepared... EDIT: can he?
I do have aerial troops (Half-fiend trolls & half-fiend ice trolls), and they will start dropping Tanarukk (the bulk of the army is tanarukk) on the walls to fight the defenders.
"Prepared" isn't a word that applies in this situation. It is a Druid-based Hathran, inside Rashemen. She can cast Wall of Thorns as many times as she has 5th level and higher spell slots, thanks to spirit magic. There are several Hathran present.
I think what I'm going with as the "back-up plan" is 15th CL scrolls of Greater Stone Shape. A 45-degree angled section of the wall 30 ft long, 5 ft high (measured 90 degrees from the 45-degree angle), and 1 ft deep can be "peeled" away from the wall at 90-degrees along the long edge, and turned into a stairway up the face of the wall.
Seriously, you having problems thinking outside the box?
The problem is the number of casters they have, and the amount of time to prepare for this. Their initial plan is to bust down the walls and get through in time to disrupt a ritual. They won't have the resources for 1000 scrolls of whatever.
Their casters consist of one 9th level Spirit Shaman with Practiced Spellcaster (CL 13th),
Seven 10th level Archivists with Practiced Spellcaster (CL 14th),
Fourteen 6th level Wizards with Practiced Spellcaster (CL 10th),
and one hundred 4th level Archivists with Practiced Spellcaster (CL 8th).
The idea of a mobile Unhallow spell is interesting, though I don't think the rules actually allow it...
There is the Darkskull in the DMG, but that's more than just a casting of the spell.
Dark Way may actually be what I need, and they've actually got enough spellcasters to pull that off.
The army is made of trolls? Just push the 1st wave into the thorns, and the second wave passes thru walking on the bodies of the 1st wave. Then the 1st wave pulls themselves up, regenerates, and continues on.
Or they could just hack & slash their way through.
They've only got about 150 regenerating troll. The bulk of the army (2400+) are Tanarukk; there are also an assortment of other creatures (ogres, ettins, hags, winter wolves, etc.) numbering in the hundreds.
Hacking and slashing through takes 10 minutes per foot...
It will alter the flavor of the battle somewhat, but I think I will rely upon a combination of aerial drop-offs (I used this tactic before, just like RHoD does at the massacre of Drellin's Ferry), massive use of Dark Way, and a few scrolls of Greater Stone Shape to deal with this.
They can have the wizards weaken a section of defenders with a fireball or two, and then drop off troops to secure that section of wall, and simultaneously mass assault via Dark Ways, and take control of the top of the wall, then use Greater Stone Shape to secure a permanent pathway up the outside of the wall to move the rest of their troops up.
My concept of treating the "Streets of Blood" encounter as if the PC were defending the breach in the wall itself will be thrown out the window, but it can instead be redirected to the initial tanarukk movements off the wall.
