In the wake of the announcement of the next edition of D&D, I've been thinking a bit about what parts of 4th Edition might be worth keeping. The rules for minions, elites and solos are a good concept, but they're limited in that they don't allow for a standard monster to be converted into a minion, and conversion into an Elite or Solo is possible but only in specific ways. The edition's focus on the “monster math” creates balance at a high cost in flexibility, in my opinion.
So I decided that I could adapt the idea to Labyrinth Lord, and having a simpler base system would allow for easy dynamic adjustment. This system allows the DM to add “templates” to monsters and NPCs. With templates in play it's best to have non-templated “normal” monsters have 4 HP per HD (instead of the usual range), but this isn't essential.
HP: 1 per HD.
Attack: +1 to hit and damage.
HP: 8 per HD.
Attack: +2 to hit and damage.
Saves: +2 bonus.
AC: -2 bonus.
XP: Each Elite is worth double usual experience.
HP: 15 per HD.
Attack: Two sets of actions per round, at +3 to hit and damage.
Saves: +4 bonus.
AC: -2 bonus.
XP: A Master is worth four times usual experience.
Special: Attacks that normally instant-kill instead cause the loss of 1d8 HP per HD of the Master (allow the attacking player to roll). Attacks that normally paralyse or debilitate (including mind control) instead only cost the Master it's next round's actions, then it resists the effect.
Pawn: DMs may add this template to groups of enemies who are weaker than the PCs. The reduced HP allows them to be killed quicker (usually in one hit), but the attack bonuses make them a more credible threat while they live. This allows battles against hordes of enemies to be less tedious and more decisive. Don't use this template for monsters who only have half a Hit Die or less (like kobolds) – they have few enough HP already to die easily in one hit.
Champion: This template allows an easy way to boost a monster to a “mini-boss” status, without requiring any special XP recalculations because it simply counts as two of the normal kind. Compared to two normal monsters, one Champion may be harder to kill (it only takes damage once from area attacks and has stronger AC and saves) but the attack bonuses aren't as good as having two sets of attacks, so Champions are good for stand-up hack-and-slash matches.
Master: Major “bosses”, Masters are intended to be able to face a party alone, but can be used with some lesser allies too. They are champion-Champions, and similar concepts apply to their game mechanics. They are not as deadly on attack as four non-templated monsters all attacking together, but their very high HP keep them in the fight where the four basic monsters would soon lose some of their number and therefore have weakening offence. Their special defence ability keeps them from losing anticlimactically to a single spell in round 1, yet still allows special-effect magics to play a major role in the fight.