Huge low CR creatures?

[Jastermereel]

I'm trying to set up a climactic encounter with my players that involves them in the ruins of a city block taking out a creature of considerable size that has been the brood mother for assorted pests they've had to deal with recently.

The only problem is, they'll be around level 4 when they find it and I'm hoping for it to be at least large, if not huge and I can't find many creatures of that size that wouldn't cause a total wipe. They won't be fighting on even ground with it, likely they'll have to use the ruined walls as cover that it can't get into, but that wouldn't help much against a creature too far above an appropriate CR.

An advanced Ankheg could fit the bill, but I figured you lot might have some more creative or more appropriate ideas.

[Grumman]

I was going to suggest a Half-Ogre Goliath, but it sounds like you're looking for non-humanoids.

[Johel]

http://www.penpaperpixel.org/tools/d20monsterfilter/index.php

Animated Object, Huge 5
Constrictor Snake, Giant 5
Crocodile, Giant 4
Cryohydra, Five-Headed 6
Hydra, Five-Headed 4
Hydra, Seven-Headed 6
Hydra, Six-Headed 5
Monstrous Centipede, Huge 2
Monstrous Spider, Huge 5
Ooze, Gelatinous Cube 3
Orca 5
Pyrohydra, Five-Headed 6
Shark, Huge 4
Skeleton, Advanced Megaraptor 6
Snake, Huge Viper 3
Tendriculos 6

EDIT : went to fast.
For the brood, here you go.
Spiders ? Centipedes ?
A Huge Monstrous Centipede is CR 2
Add a Centipede Swarm (CR 4) and that's it.

A Colossal Monstrous Centipede is CR 9. If it's alone, they can make it.

[hamishspence]

Huge centipedes are CR 2 and Huge Spiders CR 5- might make passable "brood mothers"

EDIT: Ninjaed.

[Xzeno]

I shall put forward the Tendriculos. It may be a tad tough (that regeneration's a bite) for level four, but it's Huge. It also happens to be my favorite monster in D&D.

[Kelb_Panthera]

Remember that if this is a "boss fight" you can use a creature of up to CR 8 and expect it to be reasonably survivable for the party as a whole. Though at CR 8 you'll probably see at least one character death.

[Jastermereel]

Thank you all for your responses.

As a follow-up, how does one get a good sense of CR of an advanced creature? HD alone seem a small change and increases in size seem rather dramatic. If I don't use one of the basic vermin with variations at each size category, how should I get a good sense of the challenge it poses?

[jiriku]

The SRD tells you how. (http://www.d20srd.org/srd/improvingMonsters.htm#advancedMonsterChallengeRati ng)

The system's not perfect, but it's a good starting point.

When using the table in the link provided, I find that monsters I advance myself are somewhat tougher than stock MMI creatures of equivalent CR, but that's probably because I optimize feat and skill selections and incorporate splatbook options.

[Sophismata]

Surprised noone mentioned the Giant Crab (http://www.wizards.com/default.asp?x=dnd/fw/20040221a). Technically, it's low CR.

[Riffington]

Two options if you want to use something over-CR'd:
*A lot of huge creatures have difficulty with ranged attacks. In a city, the characters may be clever enough to get it to chase one character while the others pelt it with attacks; when it finally catches her, she may be able to disappear by spell or by climbing in a window/door that is too small for the creature.

*there's never a rule that enemies start at full HP. If some crazy NPC attacks it before the players get into the scene (or attacks it with them and quickly is killed), the creatures will be much easier to slay.

On the nature of NPC allies: it is always highly unsatisfying when the PCs try their best to defeat an opponent, fail, then have an allied NPC succeed. The reverse is not true. An NPC who dies valiantly weakening an opponent, which then is still a challenge for the PCs to defeat is neither unsatisfying nor annoying.

[Quietus]

The only time an actual size increase is really frightening for a monster is when it really puts that size increase to use. Something with a pair of claw attacks, for example, is only going to get +3 to attacks and +4 to damage (plus die increases and higher base, admittedly) for going from large to huge based on hit dice, and some extra HP. Maybe reach. Now, if you select feats that make use of that, or go power attacking with the increased base, with a two-handed weapon, THEN it really starts to feel bigger and more terrifying.. but if you're just looking for something BIG, then you could easily just increase its size.. or hell, take whatever CR 3-5 monster has stats you like, and reskin it into a 20-foot tall, massive, quivering mound of flesh brood mother monster. That happens to have the stats of, say, a zombie.

[Jastermereel]

Jiriku - Thanks for the link; I'd not seen those details before. Also, I'm thinking of opting for interesting but not particularly powerful feats so that they enhance how it plays out but don't seriously toughen the encounter. That is, Mighty Roar is more interesting than Cleave because if I make use of the latter, something is going seriously wrong, whereas the former gives them a heads up that they're dealing with something powerful but doesn't put them in considerably more harm.

Interesting points there Riffington. I'm half expecting the former to be the way it'll go down. The latter might be nice to amp up the theatrics and I think I know just the NPC(s) to use in the developing scenario.

Thanks to all!

[Kelb_Panthera]

Starting point for advancing by HD is +1 to cr per 2HD increase, +1 extra on size increase. Be warned that this only works for creatures that are already designed as bruisers and even then only within the core ruleset. Splatbooks and optimization can change the CR significantly. Even just fiddling with a stock monster's feats and skills can increase their CR when you get enough splat involved.

[Zaydos]

Starting point for advancing by HD is +1 to cr per 2HD increase, +1 extra on size increase. Be warned that this only works for creatures that are already designed as bruisers and even then only within the core ruleset. Splatbooks and optimization can change the CR significantly. Even just fiddling with a stock monster's feats and skills can increase their CR when you get enough splat involved.

It actually varies by creature type. +1 per 2 HD is for dragons and outsiders (I think), +1 per 4 covers several creatures (oozes, vermin) and some have +1 per 3.

[Jastermereel]

Aye, it's as follows according to that SRD link:
+1 CR for each associated class level
+1 CR per Two Dragon HD, outsider HD, and nonassociated class levels
+1 CR per Three Animal, magical beast, and monstrous humanoid HD
+1 CR per Four Aberration, construct, elemental, fey, giant, humanoid, ooze, plant, and undead, vermin HD

[Skaven]

You could use a higher CR creature and give them a favorable terrain advantage.

Terrain advantage is a huge factor, and could give them a fighting chance against a creature they normally couldn't survive.

[dspeyer]

There's also the udoroot (http://www.d20srd.org/srd/psionic/monsters/udoroot).

If you want something with a natural brood, though, Snakes, Crocodiles, Spiders and Centipedes are probably the best options, since they have smaller versions statted.

[Dr.Epic]

What's the CR on huge animate objects? I think it's low.