Did you remember to add in stuff like impact hits from the couldron, death hag (potentially with either strenght sword of more attacks sword), 5+ ward on witch elfs, rerolling ALL their To Wound rolls and armour piercing due to AP banner magic banner?
They have a craptastic amount of special rules. 60 attacks rerolling to hit, rerolling to wound and with armour piercing and poison?
Also assuming 45 attacks it would generat roughly 9½ wounds and not 15. You forgot the ward
I did not forget the ward save, witch elves do not come with one, but since they are usually fielded with a cauldron and you asked about adding more items into the witch elf unit then I present the following:
My 1st addittion to the Saurus Warriors tactica, it is my personal favorite way to deal with witch elf deathstars (The unit you mention is almost 900 points). The set up I have below is something I run often but only combine the characters into the unit if fighting something like a witch elf deathstar, I usually keep them in a cold one bus, run solo, or even add them to a Krox unit depending on the situation. So remember your mileage may vary but the strategy part of this tactic is done during deployment and then the movement phase before you get charged (unless you deploy 5 wide instead of a horde), everything else is the dice lol.
Mathammer Grudge Match round 2
40x Witch Elves w/FC and Razor Standard
Hag with Cauldron, Brew, Cry, Ogre Blade
Total Points 870
40x Saurus w/FC hand weapon and shield
Scar Vet Cowboy, BSB, Dragonhelm, Obsidian Trinket, Other Tricksters Shard, LA, GW
OldBlood Cowboy, Pirhana Blade, Glittering Scales, Luckstone, Potion of Strength
Total Points 872
Witch Elves get the charge, saurus moved into charge range and reformed to 5 wide 8 deep plus 4, both cowboys are on the left side with the oldblood on the edge. Cauldron is in the middle with 3 and 4 witch elves to either side, the charge maximizes models by getting 5 witch elves btb (1 with only oldblood as target) along with the cauldron. Oldblood used potion of strength, witch elves could decide not to charge but then saurus will next turn so they would lose impact hits and charging CR.
-------------------------------------------------------------------------
Witch Elves Turn 1
Impact Hits = 3 dead saurus
Hag = 6 attacks = 5 wounds = 4 dead saurus
Witch Elves (With attendents)(Against Saurus) = 32 attacks = 18 wounds = 10 dead saurus
Witch Elves (Against Oldblood) = 6 attacks = 2 wounds = 0 wounds
Total CR = 21
Lizardmen Turn 1
Saurus = 8 attacks (6 OTS) = 3 wounds = 2 dead witch elves
Cold One (Against Witch Elves)(OTS) = 2 attacks = 1 wound = 1 dead witch elf
Cold One (Against Cauldron)(OTS) = 2 attacks = 1 hit = 0 wounds
Oldblood = 6 attacks (+1 PF)(Against Cauldron)(OTS) = 6 wounds = Dead Cauldron
Scar Vet = 5 attacks (+1 PF)(Against Hag)(OTS) = 2 wounds = Dead Hag
Total CR = 17 (Lizardmen are steadfast)
-------------------------------------------------------------------------
Witch Elves Turn 2 (Lost hag and cauldron so no double frenzy or re-roll all wounds)
Witch Elves (Against Saurus) = 25 attacks = 11 wounds = 6 dead saurus
Witch Elves (Against Oldblood) = 10 attacks = 3 wounds = 1 wound (Had to happen sometime)
Total CR = 7
Lizardmen Turn 2
Saurus = 9 attacks = 4 hits = 3 wounds = 3 dead witch elves
Cold Ones = 2 attacks = 1 wound = 1 dead witch elf
Oldblood = 6 attacks (+1 PF) = 4 wounds = 4 dead witch elves
Scar Vet = 4 attacks = 3 wounds = 2 wounds = 2 dead witch elves
Total CR = 15 (Witch Elves lose frenzy, and need insane courage to stay)
-------------------------------------------------------------------------
Witch Elves Turn 3 (no frenzy)
Witch Elves (Against Saurus) = 20 attacks = 9 wounds = 5 dead saurus
Witch Elves (Against Oldblood) = 8 attacks = 3 wounds = 0 wounds
Total CR = 9
Lizardmen Turn 3
Saurus = 9 attacks = 5 hits = 3 wounds = 3 dead witch elves
Cold Ones = 2 attacks = 1 hit = 0 wounds
Oldblood = 6 attacks (+1 PF) = 4 wounds = 4 dead witch elves
Scar Vet = 5 attacks (+1 PF) = 3 wounds = 3 dead witch elves
Total CR = 14
-------------------------------------------------------------------------
Witch Elves Turn 4 (17 left)
Witch Elves (Against Saurus) = 15 attacks = 7 wounds = 4 dead saurus
Witch Elves (Against Oldblood) = 8 attacks = 2 wounds = 0 wounds
Total CR = 5
Lizardmen Turn 4 (8 left plus characters, after witch elf turn 4)
Saurus = 9 attacks = 4 hits = 3 wounds = 3 dead witch elves
Cold Ones = 2 attacks = 1 hit = 1 wound = 1 dead witch elf
Oldblood = 6 attacks = 4 wounds = 4 dead witch elves
Scar Vet = 5 attacks = 3 wounds = 3 dead witch elves
Total CR = 14
-------------------------------------------------------------------------
Witch Elves Turn 5 (6 left)
Witch Elves (Against Saurus) = 10 attacks = 4 wounds = 3 dead saurus
Witch Elves (Against Oldblood) = 2 attacks = 0 wounds
Total CR = 4
Lizardmen Turn 4 (6 left plus characters, after witch elf turn 5)
Saurus = 8 attacks = 4 hits = 2 wounds = 2 dead witch elves
Cold Ones = 2 attacks = 1 hit = 0 wounds
Oldblood = 6 attacks = 4 wounds = 4 dead witch elves
Scar Vet = 5 attacks (Nothing left to attack)
Total CR = 8
If the witch elves decided to challenge with a champion then accept with your champion, if the cauldron challenges accept with your oldblood and wreck face, don't challenge yourself or your oldblood/scarvet may be hitting a champion which is not worth it.
*Note: I play without a slann almost all the time, so my list will normally include 2x oldblood and 2x scar vets, if you play with a slann then for pete's sake just buff your saurus with wissans/hand of glory/enchanted blades etc and they will do much better. But I just assume magic is going to bomb for me when I need it so I build lists without it now and if I get it off then awesome, if not then I already know what to do.
Also I would in this situation keep my cold ones to the left of my saurus block to give a good LoS if needed and charge them in on my turn to further inflict massive damage and run down the fleeing suckers. I do not include this in the tactics as your enemy always has a say in your plans so I figure worst case your cold ones are dead or playing with some other elf at the moment.