D&D 5E What monsters in 5e overshoot or undershoot their CR?

[Nebulous]

I did a CR 8 hydra last night, and the 5th level party stomped it.
Maybe I read it wrong, but fire damage stops all regeneration abilities - and fire damage is VERY common. And to even be able to regenerate a lost head, a head has to be chopped off (inflicting 25 points in a single turn).
So the party cut off two heads, but it was never able to regenerate due to fire damage.
I'm guessing a hydra dies at 0 hp even if it still has heads "alive?"

I had a hydra attack the party a few sessions ago while they were in canoes in an underwater cave. They were all 7th level but ran (rowed!) for their lives, it was going to be a TPK if they stayed, they had no way to effectively fight back if they got dumped in the jet black cold underwater river, it would have picked them off one by one.

If they'd been on land, or able to use any kind of ranged attack or get away from it they would have destroyed it, but it was in its element and at a huge advantage. Even so, they (the PCs) didn't know to use fire, so it would have just kept growing heads.

 

[Retreater]

I had a hydra attack the party a few sessions ago while they were in canoes in an underwater cave. They were all 7th level but ran (rowed!) for their lives, it was going to be a TPK if they stayed, they had no way to effectively fight back if they got dumped in the jet black cold underwater river, it would have picked them off one by one.

If they'd been on land, or able to use any kind of ranged attack or get away from it they would have destroyed it, but it was in its element and at a huge advantage. Even so, they (the PCs) didn't know to use fire, so it would have just kept growing heads.

My PCs didn't know to use fire either (being new players), but they just got lucky that their wizard is always "fire goes boom."

 

[Nebulous]

My PCs didn't know to use fire either (being new players), but they just got lucky that their wizard is always "fire goes boom."

My players "knew" but they're old hat. As an aside, we are running Tomb, and they have access to Volos' Guide to Monsters (an actual copy Volo sold them) so whenever they meet a monster in the guide, even in the middle of combat, they like to look up all the stats and weaknesses. It's rather annoying!

 

[S'mon]

So turned into a wraith? I would love to do that to a PC lol

Yeah, it was awesome - she was an elf princess, he stepped out of a picture in his throne room and stole her heart... she became the wraith-king Maeglor's wraith queen.

 

[S'mon]

By the monster design guidelines, Orcs should be CR 1 (defensive 1/8 + offensive 2 = 1).

How are thugs and lizardmen?

I suspect the issue is that in practice the Orc's very weak defence (AC 13 & 15 hp) does not really compensate for its decent offence (ATT +5/d12+3). In play it's clearly above CR 1/4 but weak compared to most CR 1/2, even offensively weak CR 1/2 like the standard gnoll.

 

[Matrix Sorcica]

Thug and lizardfolk checks out.

 

[S'mon]

Thug and lizardfolk checks out.

If the system rates Orc higher than Thug, that indicates the system doesn't work very well. IME the Thug's big hp tally and 2 attacks with advtg make it much more dangerous despite low AC.

 

[Nebulous]

Yeah, it was awesome - she was an elf princess, he stepped out of a picture in his throne room and stole her heart... she became the wraith-king Maeglor's wraith queen.

Effing awesome!

 

[Matrix Sorcica]

If the system rates Orc higher than Thug, that indicates the system doesn't work very well. IME the Thug's big hp tally and 2 attacks with advtg make it much more dangerous despite low AC.

Both the Orc and the thug hp fall in the same range for CR calculation. Same with damage. Thus the Orc's better AC and attack bonus makes the difference. So you're absolutely right. The system doesn't work.

 

[Nebulous]

In general, all the 5e low level common baddies need to be a little tougher. Hell, even some of the bigger ones, they dish out too little damage to be a threat. To mitigate this, having them attack in huge swarms seems to help. It's easily houseruled by a DM familiar with running games, which I do all the time, but per the book, it does have some issues.