D&D 5E As a DM, what monster abilities do you find difficult to run?

[J-H]

If you're playing in person and using folded notecards to track initiative, add one for Initiative 20 (lair/environmental actions), and 3 small ones for Legendary actions as reminders.

 

[Iry]

Indeed. Intelligence does seem to get fetishised quite a bit in fantasy / sci-fi circles as the be-all and end-all of every character and conflict.

The biggest problem is that characters are dumb. Not the player, but the characters. We only have a limited amount of time to play the game, and need to keep things flowing. That means a huge amount of intellectual power and information gathering cannot be applied, and even when it can, the characters often disagree on a course of action because they lack good resolution skills.

Even groups of brilliant engineers who meticulously plan every move ultimately answer to The Dark Tyrant of Limited Time.

 

[Blue]

Remembering to use legendary actions every round.

 

[77IM]

Auras... especially if they trigger on the PC's turns, it's too easy for me to forget about them.

Immunities... for some reason, I remember Resistances really well, but not Immunities. Maybe it's because with Resistances there's something for me to do, but with Immunities all I do is say "nu-uh."

Multiple stateful monsters... like, it's OK for the big bad monster to have a recharge ability or some innate-spells-per-day, but when I'm running like 8 monsters and they each have this, it becomes very hard for me to track which ones have and have not used which abilities.

Blindsight vs Stealth... I still don't have a great answer to this.

 

[Todd Roybark]

On top of this, the new standard appears to be to include a relevant spell description in the actions, like chromatic orb from Auril's first stage

Yes, the Stat blocks are becoming more DM friendly, and have been even going back to VGtM.
I also find it much easier to swap out a spell from the default creature entry, then having to redesign a new monster power.

5e stat blocks should at least contain the book and page number of the spell.

Spellcasting creatures are more difficult to prep for, but once the prep is done running them isn't too hard.

Upcast spells and use your big slots first. Always modify the default spells, always take and cast Shield, (if appropriate), and use boxes and checkmarks to keep track of spell slots used.

For a caster like Ras Nsi or Halaster Blackcloak, just plan out some combos, and you can use whatever spell or effect you want, outside of the combos. Any caster that has been around for a century or two can plausibly know anything.

 

[Nilbog]

Definitely spellcasting, to remember the spells effects and to use them efficiently I find really difficult. I tend to strip out all but the key spells and like @Zaukrie list them as abilities

 

[Ruin Explorer]

I disagree a bit on this. Although there are a lot more monsters that have spells, I think for the most part they are there for flavor / world building and can be easily ignored on purpose. What I mean by this is that the CR of the monster, unless it is primarily a spellcaster, is not determined by the spells it has. They are there for an extra layer if you want them or need them, but you can run the monster completely fine without them. On top of this, the new standard appears to be to include a relevant spell description in the actions, like chromatic orb from Auril's first stage:

View attachment 126676

I think this is a good compromise. You have a spell you are likely to need stated out for you, and then some flavor spells you can use if you want to, but you don't need to.

I think what they're doing in there (presumably in Frostmaiden?) is good, but it's not how it's been done historically, at least not in a lot of cases.

I don't agree that "for the most part" monster spells are for world-building, certainly not the in the books I own (which is all the actual monster-books and most of the setting books, but not the adventures). On the contrary, by far the majority of monsters which have spells seem pretty reliant on them, and the spells are often poorly called-out. It's not a few monsters, either - it's a large number, and sometimes they have quite an array of spells. You can usually get somewhere by starting at the top of the list, spell-level-wise, but it's a messy, clumsy way to do things, and the balance is dodgy. You say the CR doesn't include the spells - I don't agree - but I would say it's inconsistent. There are some monsters where, if you don't use the spells, they're nowhere near that CR, but there are others where it just appears to be a "bonus". CRs in 5E are generally pretty dodgy, way behind 4E in reliability, but at least they're way, way ahead of 3.XE, where they were actively misleading (as in, you'd get a better result eyeballing stuff than using 3.XE CRs, and two monsters of objectively extremely different power levels could easily have the same CR because of the weird-ass way it was calculated).

This blog can help. The Monsters Know What They’re Doing - Ready-to-Use Tactics for D&D 5E
Even if you don't agree with his tactics, he explains his reasoning and assumptions, so it's easy to work out your own

I haven't read all his stuff, but I think he falls into the trap of stats = personality pretty often, and often totally fails to account for the mindsets, cultures, and so on of the monsters in the tactics he lists. I think he's representative of the cultural problem D&D has here with this insistence that DMs have to use certain tactics for certain monsters of they're in some way "bad DMs" (some of his pieces very much have that vibe, especially earlier ones). They're full of weird assumptions like that creatures with Darkvision always prefer to fight at night, too, which often make no sense holistically (for example, in situations where most creatures the monsters interact with have Darkvision, there's no advantage, and he seems to forget that even creatures with Darkvision still get Disadvantage on Perception checks in darkness, for example).

All that said, he does go through the abilities/spells a monster has systematically, and whilst his conclusions are almost always a bit metagame-y and facile, he does sometimes come up with some kind of golden idea. Re: explanations, he usually explains, but a lot of his pieces involve so much assumption that he forgets to explain certain things. I'd be cautious of pointing less experienced/confident DMs to his stuff because I think it's such a narrow mindset.

 

[dave2008]

I think what they're doing in there (presumably in Frostmaiden?) is good, but it's not how it's been done historically, at least not in a lot of cases.

That snip was, but it started well before Frostmaiden. That was just the easiest to find as it was fresh in my memory.

I don't agree that "for the most part" monster spells are for world-building, certainly not the in the books I own (which is all the actual monster-books and most of the setting books, but not the adventures).

We will have to agree to disagree. However, please note that I qualified my statement to monsters that are not primarily spellcasters.

I make a lot of 5e custom monsters (over 400 posted on EnWorld's forums) and I check them against the MM and DMG a lot. What I find is a lot of monsters with innate casting don't rely on those spells for their CR calculation. For example:

The pit fiend as a really awesome at will spell, it can cast fireball. Surely that figures into is CR? Nope, the fireball damage is less than its multiattack damage option. Is it useful, absolutely. It is fireball after all. Could it be a great attack in the right circumstance. Absolutely. Would it be a shame to forgot it? Possibly. However, the pit fiend works just fine (CR wise) without it.

I find this to be pretty common, but I also find the CRs in the MM to be fairly accurate (with some exceptions) when you account for all the features and traits. Others do not agree.

 

[robus]

Lair actions....because they aren't in the statblock. Fortunately, its only been one monster so far.....

I do find transcribing the stat block into an abbreviated form helps familiarize myself with the monster and makes me think about how it might behave. It also lets me add lair actions into the stat block (as they should be).

It is a bit ridiculous that WotC makes us do all this work to make their stuff functional during the actual game though...

 

[pogre]

I really appreciate adventures that include a line or two about a monster's tactics and motivations. I try to do the same in my homebrew. Motivations give a clue on whether a monster is likely to retreat at the first chance, surrender, or fight to the death. Naturally, I can figure out all tactics and motivations on the fly, but given some intentions from the author makes things a bit easier.