So, I'm new to the game (Been playing 40k, WFB and, recently, AoS for years, and finally decided to dip my toe in to Lord of the Rings), and since I've always been a big fan of more bestial armies (Love my 40k 'nids and my AoS beastmen) I was wondering if an army made up almost entirely of beasts, like giant spiders, wargs, bats and etc. would be at least somewhat viable. Would probably add Druzhag, since his spell is excellent for buffing beasts from what I can tell, and maybe Shelob, since she is both an awesome giant spider and also buffable by Druzhag, but other then those two I have no idea what kind of composition this would look like. Would think a Warg Chieftain and Spider Queen would be necessary, but again, I'm not sure, and I have no idea what ratio of spiders, wargs, and bats I'd need to be efficient. So, any advice (Or advice against this idea, if it's that bad) with building an army like this would be much appreciated.

It is somewhat, and has been done many times before of course. Naturally, having a very low model count means you will struggle in many of the scenarios, while you will perform very well in lords of battle and also a few of the broken scenarios like seize the prize and the attacker and defender one or whatever it’s called cos you can move about very quickly with spiders and bats warms and the like. Monsters are good, but are liable to being surrounded and taken down, and so are best used as a support to infantry in my experience.

The Moria and Angmar book is the one you want. It has all the profiles and rules for Bat Swarms, Wild Wargs, Cave Trolls, Buhrdur (a named Troll Hero), Warg Chieftains, Giant Spiders and the Spider Queen. My advice would be to have a group of Orcs or Goblins in there with them to add numbers, spears and the like. Luckily they're in the same book.

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Gondor: 2339pts
Rohan: 1318pts
Dwarves: 2482pts
Elves: 1091pts
Mordor: 2305pts
Isengard: 1762pts
Moria: 1463pts
Evil Men: 381pts