Seven red squares of 20'
anyone moving...good luck
Okay, Maur cannot see all the foes. His darkvision doesn't allow him to see beyond 90 feet and the light doesn't go beyond 70 feet. While I showed where all the foes are on the map, Maur cannot see all of them! With his darkvision, he can only see up to the first line of ghasts, not anything beyond that, although once Phar points out where the hell hound are located, he can see them more clearly and the ghouls and ghasts closest to them (but not Tarrak).
Only
Phar can see them all due to his low-light vision. He can give Maur some direction, which was the point of my post, but I want a Knowledge (Dungeoneering) check, at the very least, for Maur to estimate where to place his own spell. (You can use his Stonecunning racial bonus for the roll.) Maur also has the benefit of having come through this cave on his way back to Carnell, so that's another +2 circumstance bonus to your roll.
While you know where Caerth's spike stones are laid out, Maur doesn't have that exact knowledge. Like the bad guys, he can't see them either. Caerth can tell him ahead of time where he's going to place his spell effect, but Maur still has to
visualize it. So, please roll the check. While you can suggest a different skill, I think that knowledge skill is the best option and Maur has 1 rank in it.
If another PC with at least one rank in Knowledge (Dungeoneering) is adjacent to Maur at the time of his casting, that character can use Aid Another (DC 10) to improve Maur's odds of success. Looking at the map and the PC sheets, that includes both Angus and Phar.
Phar - Knowledge (Dungeoneering) - Aid Another: 1D20+8 = [8]+8 = 16 (success)
So, that is a +2 from Maur's stonecunning, +2 from Phar, the +2 circumstance bonus, and if
@Tellerian Hawke's Aid Another roll is successful, you could have as much as +8 to the roll, but you already have a +6.
The base DC is 20.
If Maur hits that mark, he won't overlap with Caerth's spell. He can reasonably hit all of the mindless undead, the hell hounds, and the two senior acolytes with such a roll. If you manage to roll over 25, then Maur can place the spell effect exactly as you have it laid out. If not, then we roll randomly twice (1d4) as to where Maur puts the two extra squares you've placed beyond Maur's visual range. (I'm not going to worry about the square below the hell hounds unless you want to change its position.)
On a roll of one, Maur gets the monstrous ghast standing next to Tarrak. On a roll of 2, he gets Tarrak. On a roll of 3, he doesn't get any of them. And on a roll of 4, he gets the elf. If the same number comes up more than once, the die is rerolled.
If Maur fails the check by 5 or less, then he overlaps his casting with Caerth's but only by one square. If he fails by 10 or less, the overlap is two squares. The other three 20-ft. squares will be rolled for randomly using the same process, but the roll will be 1d6 and there will be overlap depending on how much the check failed by.
