Mercenaries can be hired to aid your raiders. They will act just like the raiders but when they die, they won't come back.
Brian the Faithful
Brian the Faithful is a holy warrior and costs 1,500 gold to hire.
He has a passive buff Spririt of the Righteous, which increases the damage of all raiders by 10.
His experienced version has higher base stats, costs 2,200 to hire and, in addition to his damage buff, also has the ability to increase the combat speed of all the raiders for 60 seconds.
How to unlock:
To save gold, wait to hire him until after you've defeated everything except Anubis in the raid (you will need to cancel the raid after hiring him.) This is only recommended if he has a difficult time surviving the other bosses.
Check the prophecy Mercenary Upgrade: Experienced Holy Warrior to see the current progress.
Vikar is a necromancer and costs 900 gold to hire.
She will spawn a skeleton periodically, which will fight alongside the raiders for a short period.
Her experienced version has higher base stats, costs 1,900 gold to hire, and will spawn 2 skeletons instead of 1, which will stay alive longer after being summoned.
How to unlock:
Summon 10,000 skeletons.
This does not have to be done all at once. Check the prophecy Mercenary Upgrade: Experienced Necromancer to see the current progress.
The skeletons she summons can one-hit the monsters on farm map 7 (a popular farming map.) Hire both necromancers for maximum farming efficiency.