D&D 3E/3.5 3.5 ECL vs CR Differences

[Empirate]

This is the most important thing, right here. CRs are mostly just a guess and compare game. On the plus side, CR guessing is a pretty forgiving hobby, so if you are off by a CR or two either way, it should not affect play much.

Forgiving hobby? You obviously err on the side of caution when estimating a monster's power, and I commend you for it. But if you think along the lines of "well, this monster is about CR 7, my 4th level group should be able to handle it as a bossfight", and your CR is off by 2 in the wrong direction, you might have a TPK on your hands.

 

[freyar]

The Pathfinder SRD also has stats for CR comparison that are pretty reasonable for 3.5 as well (maybe slightly tough at a given CR level). I will say that Paizo doesn't always follow these guidelines in its own monsters, so treat these very loosely.

But, yes, comparison is still the prime way to do it. It's how we decide on CR for conversions in the Creature Catalog.

 

[Michael Silverbane]

Forgiving hobby? You obviously err on the side of caution when estimating a monster's power, and I commend you for it. But if you think along the lines of "well, this monster is about CR 7, my 4th level group should be able to handle it as a bossfight", and your CR is off by 2 in the wrong direction, you might have a TPK on your hands.

My players are usually smart enough to realize that an encounter is too tough for them before they end up in a TPK situation... Usually. And when they aren't it is only their characters that get killed.

 

[Herzog]

CR is always an estimate, 'calculated' with a typical party in mind with level-appropriate gear. Always take into account your actual party when determining whether the encounter is appropriate.

For instance, I once horribly failed to take into account my party didn't have any area-of-effect capabilities, and was almost TPK-ed by a scorpion-swarm. I had to allow the use of normal lamp-oil as a weapon to dispose of the swarm to correct my mistake.

A good thing to look out for is the AC of the creature(s) (can the party actually hit it?), it's DR (can they do enough damage to overcome it or can they bypass it, provided they have the correct info?), and other resistances and invulnerabilities (if the party consists of arcane casters with only fire spells, a fight with a red dragon might not be the best of encounters. Even if the CR is below their party level)

 

[Wyvernhand]

The reason CR and ECL are different is because certain abilities are more powerful in the hands of PCs. Take, for example, the ability of many outsiders to Greater Teleport themselves around at will all day long. In combat, where the PCs are fighting something with Greater Teleport, it has an action cost, so every round spent teleporting is a round not spent Imploding someone. Out of combat, however, it trivializes a lot of encounters and challenges. Things like DR, SR, large amounts of SLAs, and large net positive stat adjustments are something the PCs will put to use every day in just about every encounter, while for most bad guys, its a slight change in tactics and a dead monster, and then it doesn't matter how many unused SLAs it had left over.