I thought I'd share a few ideas about Hordes to help dispel some of the steroetypes.
First, when it comes to calculating Horde Magnitude as individuals, I use (and have for quite a while, now) the following ratios:
A Magnitude of 1=
- 3 Weedy/Scrawny creatures
- 2 Average-sized creatures
- 1 Hulking creature (typically reserved for stampeding herds of Grox or Lumox)
This help when determining how large an area they cover, as well as determining the number of stragglers and fleeing individuals…and when a Player asks how many finger bones he can collect for his trophy necklace.
Speaking from a personal perspective, I've been using hordes like heaving lumpen masses of flailing angry flesh, and I feel stupid for having done so. Every Horde encounter I've included in my games could have looked so much better from the other side of the GM screen had I thought of this a long time ago.
Just because it is a Horde does not mean the individuals that make up its Magnitude are linked at the hips.
A Magnitude 40 Horde of Imperial Guard could be two 10-man units, one with a Flamer/Heavy Flamer and led by the courageous Colonel Werner Klemperer (significant attached NPC), the other with a Plasma Gun and a Heavy Bolter (in heavy Cover), both working in concert to flank a small, rag-tag band of heretics and traitorous Chaos Marines from two different directions, to drive them into cover with suppressing fire and burn them where they hide with righteous fire, thus reducing the deleterious effects of enemy Blast and Spray weapons on their Magnitude strength and still operating under the Horde mechanics. One detachment of the Horde can be engaged by the PCs, either with melee or at range, but only so much death can be dealt before you have to turn 'round and chase after the fleeing remnants (that is if the Horde as a whole failed their WP Testafter taking 50% casualties).
Rather than behaving as two 20 Magnitude Hordes, it still behaves as one 40 Magnitude Horde (in so far as number of attacks and Damage caused) but it is more versatile in terms of mobility, utility, and cinematics.