I think bloody flagellants can be pretty nifty. Because of how they're recruited, you can get a LOT of sacreds massed up, and even with just the blood bless (which is pretty cheap) those flails (2 attacks, +2 attack vs shields) do a lot of damage with the extra strength, and they already have a good chance to hit stuff. Trying to counter with other melee troops will result in massive losses, countering with archers will also eat up a lot of those squishy bowmen, and trying to wipe them out with spells is a particularly bad idea... Sure, mages generally have much better MR than other troops, but their spells will generally hit a LOT of flagellants, which means that MR gets tested a bunch of times. And mages aren't generally known for their tankiness...
The minor bless effect also has some interesting effects with some sacreds, like EA T'ien Ch'i's heavenly fire demons. Throwing weapon damage and range is generally affected by strength values, so you can pump that up a little. Jomonese tengu also get their AN lightning attacks buffed by a few points, if that's important to y'all.
Outside of flagellants, another fun pick for a blood bless is someone with those ancestral spirit battle summons. Just pop a bunch of those out and let the enemy kill themselves by striking the spirits.
Speaking of ancestral spirits, a fire bless can be pretty funny on them since they generally don't deal any direct damage, but the fire bless applies the 6 AP damage to their paralyze attack. Same deal for death bless, which also makes them hang around a lot longer (but doesn't give them the bonus attack value they desperately need).