*'''[https://www.games-workshop.com/resources/PDF/AoS_Warscrolls/AoS_Flesh-eater_Courts_WSCards_Crypt_Horrors.pdf Crypt Horrors]:''' '''Battleline''' if a Crypt Haunter Courtier is your General. Simply put, Crypt Horrors are Ogre equivalents. 4 Wounds, 5+ save. 3 attacks with no Rend and 2 Damage each. You know, the usual. These here also regenerate and get rerolls To Hit if a Ghoul King is nearby, thereby eliminating their only real weakness. Take this first. Flayers are also useful, but more gimmicky skirmishers compared to the powerful sledgehammers the Crypt Horrors are.
*'''[https://www.games-workshop.com/resources/PDF/AoS_Warscrolls/AoS_Flesh-eater_Courts_WSCards_Crypt_Flayers.pdf Crypt Flayers]:''' '''Battleline''' if a Crypt Infernal Courtier is your General. Their melee profile is the same as that of Horrors with one more attack, but with only damage 1 and rend and the chance to inflict mortal wounds. Then you see that they have a scream attack that inflicts mortal wounds equal to the bravery they beat on a 2d6(-2 on the roll if not within 3" of the target). Then you finally realize they're not meant to be powerhouses. They're harassers and tarpits, just like Razorgors for the Beastmen and are very useful when summoned via Command Ability, because they are fast enough to close the distance quickly
. Oh, and you need these because the Crypt Infernal Courtier, aka the second-best Courtier, summons them.