Interesting!
A couple of considerations: as a non native English speaker I find the use of the term "horde" to denote a single weak monster to be confusing, something like minion would have been clearer to me.
Also, these rules cover a different space than the squad template, where multiple simple creatures fight together as one. This is the exact opposite, so the GM controls individually each horde monster.
I'll make an example with the little rules given in the post to see if I got other things right.
Instead of 2 Ogres (CR 2, medium encounter for a party of 4 level 3 characters), one could use 5 Horde Ogres.
Each will have 13hp, and these attack options:
Greatclub: +6 to hit, 15 damage (2d8+6) bludgeoning, on crit save DC 14 or prone
Javelin: +6 to hit, 13 damage (2d6+6)
So these creatures have each approx 20% of the HP of the original one (59) but they hit a bit harder (+2 to each damage). As a group they have 55% of the total hp of the equivalent non-horde encounter, but they hit WAY harder (2,8x per round on average
excluding crits).
It looks like the combat could be very swingy! Either horde monsters die very quickly, or they can do
significant damage to the party.
To be honest I'm not really convinced by the increase in damage.
I'm curious to see if there's some better guidance in the final product
EDIT:
Thanks to
@W'rkncacnter for pointing out that large creatures don't roll additional weapon damage.
With that in mind, horde ogres would deal (10) 1d8+6 damage with the greatclub (+prone DC14 prone when critting) or 9 (1d6+6) with the javelin. A group of 5 horde ogres (medium encounter for 4 level 3 PCs) would thus inflict approx 1.9x the damage of 2 normal ogres, and have approx 55% of their hp.
The combat is still tricky given the additional number of attacks in total, but seems quite more manageable!
It looks for these encounters having ranged or area damage would be extremely useful. Very impactful is also the initiative order.
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