Class levels and CR.

[the Jester]

This is one of the many issues with the CR system. It's just not reliable or precise.

That said, it's a reasonable tool in many (if not most) cases.

 

[Piscivorous]

Keep in mind that unless you are playing with precisely 4 PCs, that CRs can only ever be used as a subjective guideline. You'll need to adjust CRs up and down dependent on how many more or less PCs than four are in your group.

I use a 3.5 ECL calculator to help me design the encounters in my campaign. It works very well.

 

[Theroc]

Keep in mind that unless you are playing with precisely 4 PCs, that CRs can only ever be used as a subjective guideline. You'll need to adjust CRs up and down dependent on how many more or less PCs than four are in your group.

I use a 3.5 ECL calculator to help me design the encounters in my campaign. It works very well.

Thanks for the tip. In my case I am currently working with exactly 4 PCs.

I also use the Encounter Level Calculator d20 Encounter Calculator :: Pen, Paper, & Pixel

To get an idea what CR to throw at a party. Granted... I misread the CR for my last encounter, but it worked out well. Turns out 4 level 1 PC's CAN beat a CR3 monster without too much issue(particularly if the DM can't roll well to save his life.)

 

[Dross]

Keep in mind that unless you are playing with precisely 4 PCs, that CRs can only ever be used as a subjective guideline. You'll need to adjust CRs up and down dependent on how many more or less PCs than four are in your group.

I use a 3.5 ECL calculator to help me design the encounters in my campaign. It works very well.

I would also add, 4 PCs, one each of cleric, fighter, rogue, & wizard (with the appropriate substitutions). A complete lack of one (except maybe rogue) can seriously upset that balance.

 

[Persiflage]

The party I'm running took out an Ankheg with minimal trouble. (The entire party took a total of 20 damage(they lined up for the acid spit right before tearing him to pieces) within like, 3 rounds.

I was trying to think of something to be a bit more challenging. (These fights take place in a gladitorial arena format, so they are generally at 100% resources when these encounters take place).

So, it'd be best to throw multiple weaker creatures at the party, I suppose?

What you need is... THAT DAMN CRAB! A mated pair thereof. Having a giant pool of salt water in the arena would just be gravy

It's CR 3. It has 66hp - more than twice as many as the Ankheg - and AC 19. It has 40' land movement rate and 30' swim speed. It has reach. The common low-level save-or-suck spells like color spray and sleep are worthless (grease would work if it's on land, but don't forget to give it a stability bonus for the extra legs). On round 1, it just charges the nearest creature and attacks with a claw for a total attack bonus of +12. It does 1d8+9 damage and then proceeds to make a grapple check as a free action, which it wins with its +19 modifier, and in the same round gets to do an additional 1d8+9 constriction damage.

It still has a claw free, so - for bonus points - get it to attack size a Small character in preference to all others; that way it still threatens the area around it. That's assuming that the character it got to first survived the 27hp of damage it took, of course: by now, it may well have both claws free. Then Mummy Crab gets a go... Be sure and have them start a significant distance apart so the party can't catch them both with a web or glitterdust.

If you balk at the notion of putting two of these horrors into an arena, have it instead accompanied by an anthropomorphic polar bear, tiger or giant crocodile (yes, the anthropomorphic template lowers the CR of Large creatures) with an NPC class level.

There y'go: a fair-and-balanced-yet-challenging encounter for a 3rd-level party

 

[Man in the Funny Hat]

CR's were originally set largely by feel, but I think still leaning heavily on HD to suggest what level of CR they should be. EL relies on CR "accuracy" to work. It comes down to the system just not being as reliable as it wants to be at lowest levels, or at higher levels. HD just doesn't tell the whole story, and in some cases can be far less important a factor than the exact combat abilities the opponent has.

The abilities and equipment of the PC's is also a huge factor that CR just can't take into account at all. Characters with good-better equipment, optimal combat abilities, and experienced, aggressive players will typically be undermatched by CR/EL. Combat-weak characters facing opponents run aggressively by the DM will be easily overmatched. And the vagaries of the dice will play havoc with either end.

Challenges still need to be adjusted by the DM based on what he knows of the players and their characters and this is especially true outside of the mid-level ranges.

 

[Alexander123]

I think that while CRs may help beginning DMs create encounters, for the more experienced DMs CRs are more guidelines. The way to figure out what is a challenge for your party is a number of things: party size, the degree of optimization and skill on the part of the players, the abilities of the monsters. You will definitely have to do some calculations and some tuning to figure out what monsters will present a challenge to your party.

Also take a look at Ad-Hoc Challenge Handbook (WIP).