My players are about to enter Runeforge, they opened the door at the end of our last session. One of my players is planning to retire his 14th level Brass Dragon Bloodline Sorcerer and is planning to instead play an Eldritch Knight from the Wrath wing of Runeforge.
Instead of just having my players encounter him in the Iron Cages of Lust, or in the Goldfish pond in the Vaults of Greed, I am planning to play out the battle against the Abjurers 5 years earlier that resulted in the demise of their faction.
My other players will be provided character sheets and play as some of the other Eldritch Knights in the assault and accompanied by Sinspawn and yet more of their order including Athroxis and lead by the player who is introducing the new character.
My plan is to play as the Abjurers, and attempt to defend the Runeforge room against their assault, wait until they suffer some casualties, then bring in reinforcements from the Crypts of Gluttony, and Vault of Greed to finish the Abjurers off.
With any luck, the PC's temporary characters will be dead, and the other player's new character will be knocked unconscious.
Then we begin our regular session with the PC's entering Runeforge... and eventually find the player's new PC in one of the Iron Cages of Lust, alive but badly beaten.
I'm thinking of adapting the Dwarven Abjurer from the NPC codex to use as the Abjurers for this flashback one shot equipped with Rods of Cancellation as per the description, there will probably be 4 of them with slightly differing spell lists (traps and wards are the Abjurer's bread and butter afterall), I expect it to be a hard battle, but the involvement of the other 2 factions will turn the tide of battle.
How would you plan the defence of the Runeforge from the Abjurer's perspective to make the fight challenging (assuming all Abjuration spells are known)?