Monster Hunter in D&D

[GrigoriFederov]

For those that do not know: Monster Hunter is a series that Capcom makes that does what it says on the tin: you fight monsters, a lot of them, and almost all of them significantly bigger than you are. Some questionable designs aside (lookin' at you Plesioth, ya derp), the series has a ton of really nice looking creatures of varying lethality. I started trying to stat the creatures from MH3U, seeing as the only other one I've played is MH3 and I didn't want to try statting things I'd never fought against. I think I've been moderately successful in my attempts, but there's one sticking point that I'm not quite sure how to handle. In the game the monsters lose it at certain damage thresholds and enter what players refer to as 'Rage Mode'. They get faster, hit harder, and sometimes get new attacks and combos. No problem right? The solution is in the name, just give them Rage! Well...not exactly. They don't get fatigued (necessarily) when their rage ends and the fights against these things in D&D will take significantly less time than they would in the actual games, at least I'm thinking they will. On top of that, when the monsters get tired in the game they aren't as hindered as if 'fatigued' in the D&D sense, at least it doesn't seem that way to me.

I initially left it out because most of these creatures are still terrifying without it, but some of them have iconic traits linked to rage. Specifically ones like Deviljho hulking out and Zinogre going super saiyan. Do I simply restrict its presence to the ones that really need it to mimic their behavior from the game, leave it out entirely, give it to all of them, fatigue be damned, or homebrew some other ability that fills the role? Any thoughts on this woudl be much appreciated. Also, if anyone likes I can post stats for the creatures I have stated so far. I haven't got too far yet, just up to the likes of Lagombi and Royal Ludroth. I did Alatreon for kicks, but that just turned into 'rocks fall, everyone dies' because Alatreon and inexperience. Probably more of the second.

[Gelscressor]

...and sometimes get new attacks and combos.

This vaguely reminds me of Lufia 2's system. Essentially, the party members could get "fury points" when hurt, and use these "fury points" to activate special abilities from items. The amount depended on the amount they took. Taking inspiration from that, you arguably could require them to, say, spent x amount of fury points to use ability y. Ultimately, this wouldn't be that different from a mana-based spellcasting system (or DnD's psionics system), except that, obviously, the abilities vary a lot more and that the acquisition of fury points is fundamentally different from MP/PP.

[Doorhandle]

Putting in my 20 cents:
For the changing movesets: concider making them sequential bosses. Basically, build 3 versions of the monster, make each the same Ecl as the party, and run them one after the other, which has the same net effect as a boss switching phases.

Alternatly, have the creature switch between 2 different stat blocks whenever each one goes down a certain amount of health, untill both are dead: good for a raging beastie.

Although most of the point in a changing moveset is to trip up the player's dodge patterns, which isn't much of the game in 3.5...

[GrigoriFederov]

I just ended up just using Rage. I ran things through a few times to see how it went. The Fatigue was a problem so I expanded where certain monsters could eat as a way of recovering from Fatigue. In Monster Hunter, when tired, monsters regain energy one of two ways: either raging again, or eating something. If I make it easier for them to recover stamina in this way I can just use the Rage ability. I also used a rule of thumb for when it activates. The enter rage mode every 10xCR points of damage they take. This means most of the time the more durable monsters rage more, but not more often.

There isn't any magic in Monster Hunter, least ways you're never Charming, or tossing out Fireballs (gunlance not withstanding), or Chain Lightning. When combined with the fact that a good chunk of these creatures are classified as Animals, or Magical Beasts, most will have low Will saves. This means it is entirely viable to stun lock some of them with Charms and other things like that. The group would still need to kill them, so I expect that to counteract the lack of dodging ability.

When in rage they tend to chain attacks together more frequently and in a few cases, like Deviljho's dragon breath, they gain a new attack. Generally you get this in a much more pronounced way when you move up in rank (low -> high -> G) with high to G being the biggest jump. I've toyed with the idea of the act of adding Hit Dice increasing the 'rank' of the hunt, so there is that to work with also.

[Jota]

4e had a 'bloodied' condition (at or below half health), that would also work as an alternative to a function of the CR. In the same way you only have access to certain abilities while raging under your variant, you must be blooded to use a particular subset of abilities.

If you want to introduce another phase (quarter health, or some other portion) tied to yet another set of abilities, you can always do that as well. Depending on the strength of the abilities and the length of combat, you might consider granting access to the 'bloodied' abilities for a limited duration upon becoming bloodied, and then losing those abilities after the duration expires, until they reach the next level of hit point loss (similar to fatigue and a new rage -- you mentioned disliking this, but it creates counterplay, if you care for that).

You can always implement other rules to extend fights, if you want to emulate that aspect as well. Dealing less damage (for all concerned) is one choice, whether through reduction damage or damage negation. For instance, in the classic house cat vs. wizard debate, consider the following adjustment: Weapons deal -1/+1 damage for each size category they are smaller/larger than their intended target (critical hits ignore penalties to damage). Now your monster hunters will have to wield larger weaponry to keep up damage-wise (or weapons that have special properties to deal damage as if they were larger) or attack in volume. On the other end of the spectrum, large monsters might use area of effect attacks that allow Reflex saves for reduced damage, or clever players might use readied actions to avoid the affected area entirely.

I'd be interested in reading the stat blocks to see your interpretation.