So Scrap Princess asked about creating warbeasts and how to do so in an effective way.1
The (too?) obvious answer to “how do I create warbeasts that eat people?” is necromantic compulsion. Every other answer has to contend with thorny, species-specific issues of biology, with which necromancers need not concern themselves. Find a dead beast, or create a dead beast (that is, create the deadness, rather than creating the beast), raise it up, and send it at the enemy.
The efficiency of this approach—rather than the efficacy, I think—is reliant upon just how necromancy works in your world. That is, does the difficulty in raising derive from the complexity of the mind of the being you’re reanimating, or from the mass of material you’re prying from the earth’s grip? If the former, creating warbeasts—juggernauts of reanimated bone and flesh held together by grim forces—is relatively easy. As smart as mammoths are, they aren’t as smart as the dullest farmboy, and so for less work than it would take to make a shambling ghoul, you’ve got a multi-ton war-construct that doesn’t feel pain, doesn’t spook, and never tramples backwards into your own men.
If the latter, and it’s a matter of size, well, your necromancers have some calculating to do. If it consumes the same resources (measured in wealth, man-hours, unhappy deviltry and deals struck, whatever) to create one enormous undead siege-tortoise, or X revenants where X = tortoise!mass / average!human!mass, you have to ponder your objectives and whether one siege-tortoise accomplishes those better than a minor horde of shamblers. If you have to breach fortifications to clear a lane, maybe yes; if you’re just trying to overrun enemy countryside and destroy their farming sector, maybe no.
“But hella,” you say, “Scrap asked about warbeasts that eat people.” Well, that also depends on the nature of infernal necromancy in your world. Hordemaster Romero’s shambling legions are probably better than creating a warbeast anyway. Why would you sink the resources into animating a warbeast if it’s just going to stop at first contact and chomp on the first shitheel conscript it tusk-gores, when what you really want is for it to plunge a bloody path to your objective? If your undead eat people, well, you need to make a lot of little undead, so that if one peels off to eat a brain, the rest keep going after other brains. If you make warbeasts, you want them to blindly thresh through opposition and leave it in terrified disarray. You don’t need your warbeasts to eat the flesh of the fallen foe to create terrified disarray.
So I guess this is just a roundabout way of objecting to Scrap’s premise. You don’t want your warbeasts to eat people. It’s bad generalship.
1 As opposed to a fucking awesome way, in which case I recommend the Matryoshka dogs. It’s canines1 all the way down.
1 I see what you did there.