well, point is to lock that birds from spreading and those lizzard priests from casting mark of blood. Mass lock is tied to a leadership witch depends on your intelect. The more it locks - the better. Even if it fails on some of them, some is still better than none. If it can't lock anyone then go for debufs/buffs, I can't really guess, depends on what you have in your arsenal. Most times, the harder the battle - the less units you need. I just finnished samman in 4 rounds with only 8 red dragons, and they didnt really shoot anyone, just armagedon, time back, armagedon, timeback, kill two crap units standing...Maybe you should focus on one stack tactics. Defiting those guys is a breeze comapred to what lays after them, and I haven't found a decent tactic for no loss on K'thulu except for single stact tacticts, all else is doable but it's much more complicated.
as for ancient spells, they make things easier but are not a neccessity. If you have that ancient knowledge one, that arena and boss are a good time to spend it to gain 50% more exp.
anyway, I don't know what spells you have, and your save is not compatible with my game. If you have timeback spell you can try to go single stack and count on it for round two and four, blaze the lizzards with fire or dath star, or geysir in the mean time. as long as you can keep up the mana ad troop from dieying - you are fine.
like someone said here in one of the tis & hints "less is sometimes more". In my current run I am going for the black helmet + shroud of darkness set. In last one I went all demons + some dragons sometimes. Depends. You can go to shaterra and replace your army for excecutieners or demons + archdemons. stoneskin archdemons, stoneskin demons/exec. whatch wats happens, round two, give mana spring to execut./demons (dont forget to cast that aura) and just mollest them, later resurect them (make sure archdemons dont die since they are lvl5). Like i said, i dont know what spells you have. If you have timeback, then you can wreck havoc with one unit then timeback it. Phantom spell acts like a "target in 99% of cases, draw dmg that way.
It's not too hard really, just take less stacks, define your tanks, define units that go after retaliations have been dealt with, make sure mark of blood is not on you, at least not when it matters. Stoneskined archdeamon with magic spring isn't gonna notice mark of blood on him
You can cast divine armor on demons also
One stack with stoneskin first, dmg/debuff on enemty, round two - divine armor + dmg/debuff on enemy or demon portal, rinse and repeat. It's really hard not to loose anything when you have 5 stacks that get damaged.
also, your pet is usefull for mana, wall and most important in these battles is shock ball, ball of lighninthg, whatever it is called
I think I will try for fun one stack of demons, their aura, stoneskin, divine armor and debufs on lizzards. Those guys deal next best dmg to black nights, phantom them to get aura again, since if they are only stack on field, magic spring gives you tons of mana to cast whatever you want.