For players starting Doom Tower Normal in RAID there is a trick I discovered where I used a Level 1 Gerhard the Stone which allowed me to beat the Scarab King.
The reason this worked is because when you put him as the Leader he gives to everyone +50 Resistance, which, in addition to whatever Resistance your champions have was enough for my team to resist the vast majority of Scarab King's debuffs and win the battle.
This helped me a lot because I did not need to invest extra resources to create or adapt champions for this specific boss.
So I did not need any shields. You can see my team below in battle with Gerhard the Stone as the Leader:
While I used this trick to kill my first Scarab King boss the general concept works for any difficulties. There are different strategies on killing this boss and doing it via Resistance is one way, just remember that the higher the difficulty the more Resistance you will need.
This was not the most efficient way to fight this boss, but it was the most efficient for my account because I was able to win without spending any precious resources on changing gear or leveling up dedicated champions.