I don't mean to start a treadmill discussion. I just want to know WHY monster ACs are so low. Not because it irks me (it does), but because I intend to houserule it and would like to know what were the criteria behind the decision of having the average legendary monster be hit on an 8+ by the average same-level PC, so I can make an informed decision before actually changing the rule.
My intended house rule is not THAT game breaking (I believe); I intend to make all monsters add the bonus of their HIGHEST ability score between DEX and CON to AC. This way, monsters like trolls and dragons will have a significantly higher AC without becoming gamebreaking to PCs of the same level.
However, before doing it, I want to know if there's a dev that can answer (or someone with a link to a dev's answer somewhere) what's the design reason that monster ACs are so consistently low all across. There's likely a good reason I haven't caught on to.
Thank you!
At a full 20 to a primary stat, with a +1 weapon, Archery Style and a full proficiency has a to-hit of +14. That's the highest to-hit I know possible.
Compare with an Adult Red Dragon. It has an AC of 19. That's a hit on an 5, or 80%.
If they've not a +1 weapon, that's 75% hut. Take away Archery style and that's a 65%.
65% against isn't unreasonable. And that assumes a 20 in the primary stat.
So to summarize: I don't see your problem with ACs being low.
Bounded accuracy. In earlier editions, Armor Class needed to be very high because players could get massive bonuses to their attack rolls. In 5th Edition, that's no longer the case. Similarly, the players will generally have a hard time getting to ridiculous AC totals, and mosters, even with their fairly low to hit bonuses, will still strike them with regularity.
It's a core feature of the system.
Yunru wrote:
Yunru wrote:
CorwynnMaelstrom wrote:
the reason is called "bounded accuracy" (I hate it...)
they say it's pointkess to have monsters AC scale up as CR increases just in order to match up with the pc's attack bonus which is also growing level by level.
so they decided to cut both down.
I can see a point in it. their question is "why let everything go up, if the difference doesn't change?"
my answer would be "because I don't want to be hit by low level monster when I'm high level and vice versa", but unexpectedly devs didn't take me into any account... 
Well, extrapolating from why 4e had a feat tax, is because the developers want an average of 50% chance of hitting. Plain and simple, missing isn't fun.
IxidorRS wrote:
Actually monsters don't cap out till about CR 30, at which point that "highest to-hit" only works 50% of the time.
Isirga_Eth wrote:
Yunru wrote:
To shorten combat. Legendary creatures have the ability to TPK very quickly if they survive. D&D 5e is supposed to be a matter of a handful of rounds, as opposed to earlier editions which could drag out.
(Also, I'm not gonna math it out, but I think maybe you're exaggerating that percentage or not accounting for some of the things which make a difference during actual play.)
Isirga_Eth wrote:
Kaandorian wrote:
This has not yet been mentioned in this thread. Another reason for the lower AC and to Hit bonuses of monsters is so that low CR monsters remain a threat for a larger portion of the characters adventuring career... To keep such creatures relevant, you just throw more of them at the PCs.
In 5E we can simulate the Goblins of Moria (Fellowship of the Ring), or those in the goblin caves (The Hobbit).
All those goblins were CR 1/4 or CR 1 creatures, yet combined they were an impossible challenge for the party (CR20 or above when the party was probably level 5).
A 1st level character has a chance of hitting an Adult Red Dragon, and the adult red dragon has a 25% chance of missing the 1st level fighter. This does not, however mean that the character has much chance of winning. The adult red dragon has increased action economy, substantially more HPs, and increased damage, making even a single successful hit lethal.
20 1st level characters have a chance of overwhelming a red dragon through attrition... Swarming an overwhelmingly powerful enemy is an extremely common and popular fantasy trope. Yet dispite how common the trope is, this was impossible to simulate in previous editions without absurd things like 20th level NPC classes (Commoner, Soldier, Adept, etc). In 5E, you can simulate this easily by simply throwing more creatures into the encounter to create a cumulative effect.
The reverse is also true. A single CR1 creature may not pose much of a threat to a 20th level PC, but 20 or 30 of them are capable of overwhelming the PC through attrition. In prior editions such creatures would only have a 5% chance of hitting the PC (nat 20), whereas in 5E - those same creatures have a much higher chance of success (perhaps even as high as 50%).
The only legendary creature released is the Adult Red Dragon, and a sample size of one is definitely not enough to extrapolate from.
CorwynnMaelstrom wrote:
Isirga_Eth wrote:
Yunru wrote:
Kalani wrote:
A lot of monsters I'm seeing don't have equipment on purpose. If you wanted elite fighting ogres, slap them in different armor and give them different weapons. Especially at low levels, and even so at higher levels, an ogre in ogre full plate might be a real PITA. I like that in monster stat blocks they just list the stuff that they come out with naturally. It saves me the problem of reverse engineering it to see what the equipment actually gave the monster or how I need to fix the stat block. Now I can just do some quick additions and BAM.
Isirga_Eth wrote:
Isirga_Eth wrote:
Isirga_Eth wrote:
A low level character has a cance of hitting epic monster. this is intended to allow many creatures working together a chance at defeating large threats. rather than balance monsters by making them impossible to hit they can give them more health. This allows them to better control the pace of combat. it is easier to create balance with an expected 75% hit chance for 15 damage than a 25% hit cance dealing 45 damage.
jonathonhawke wrote:
Surf's monster analysis (see http://www.enworld.org/forum/showthread.php?356956-Surf-s-D-amp-D-5e-Monster-Analysis) shows that on average, monsters are designed so that a player of level equal to their CR hits with an 8. I assume the designers, based on playtest feedback, found most players enjoy hitting most of the time. The balance then comes in with how many hit points creatures have for the appropriate CR so they last long enough even though they will get hit 60% or more of the time. If you and your players would enjoy fights that take longer, with more player misses, you should institute the houserule. If you only want to change that experience for certain special fights against certain boss monsters, give that special monster armor, or a defensive spell or ability to boost its armor class above other monsters of its CR.
Nothing was more frustrating to our Elf Avenger in 4th edition to roll to hit a target and miss with 2 dice, then reroll with Elven Accuracy and still miss fo now conceivably good reason. I mean, it's a dude in a robe with no spells, why does he have a 30 AC? (Extreme and rediculous example, but you get the idea)
Isirga_Eth wrote:
Isirga_Eth wrote:
I am generally ok with monsters having a low AC, but I think it makes feats like Great Weapon Master and the archer feat too good to pass up. -5 to hit for +10 damage is too good to pass up on the monsters.
DLfan wrote:
Isirga_Eth wrote:
One thing to consider if you up AC is that I believe hp and resistances were given to monsters with bounded accuracy in mind
So sure, hitting the CR 16 monster may not be too difficult....but is it with a magical weapon? If not, that's probably half damage. It is magical. Well you're still probably needing to remove a ton more hp.
Upping the AC by even a few points are going to make higher level monsters much more difficult due to an extending of the fight,,,giving the high level enemies more chances to use some nasty abilities and further causing pcs to expend resources in terms of class abilities in the fight.
Yunru wrote:
shadowkhat72 wrote:
If you absolutely must change the math, do so by adding magic items. These provide flat bonuses which the games math completely ignores. It is also a method of granting said magic items to the PC as a reward for successfully overcoming a more difficult challenge.
Even a low level PC who can get his/her hand on plate armour and shield has AC20. IF they have Medium armour Mastery they can get the same AC with high Dex and half-plate+ shield. If you add Defense fighting style, then they can have AC21.
Most PC's will have AC between 15 and 21 throughout their career, if you ignore magic items and buff spells etc.
Those monsters that don't wear armour (which can obviously have AC like the PC armour users) will tend to be lower AC than the PC's e.g. adult red dragon only has AC19.
From what I can tell, the higher level you go, the greater your chance to hit will be against monsters. PC chance to hit goes up through rises in proficiency and ability score rises, while the AC of monsters does not really rise likewise. Same goes for monsters - the higher the CR level generally the greater the monster's to hit bonus is, but the PC armour class doesn't really rise to keep track with these rising to hit bonuses in CR level.
This must be a deliberate mechanism - they want the chance of a miss (both PC and Monsters) to reduce as PCs go up in levels.
From a brief look through the monsters in the DMG pdf, the AC of monsters is generally lower than the AC of PCs (again look at AC19 of a Red dragon). This again is probably deliberate, as it means that PCs will be hitting monsters more than monsters are hitting them.
Clearly, the game was designed to work this way and these decisions were based, reportedly, on over 175,000 playtesters providing feedback over 2 years. It is the style that most agreed with, because they wanted to be able to use lower CR creatures in larger amounts, which is something that no other edition of D&D did effectively.
If that style doesn't agree with you and you want to change it, I would be careful. There are a lot more things that might need to be changed along with it. However, I wouldn't change AC though. I would reduce the Proficiency Bonus to Hit bonus instead. Changing proficiency bonus to Hit bonus from scaling between +2 to +6 to between +0 and +4 has the same effect of increasing AC by 2, but it changes in the direction to making the math easier i.e. 1d20 + 2 vs 16 AC is mathematically the same as 1d20 + 0 vs 14 AC thus lowering the to Hit bonus by 2: 1d20 + 0 vs 16 AC is the same as raising the AC by 2: 1d20 +2 vs 18 AC. It's the same mathematically, but it's easier and quicker to do the addittion on each die roll.
From my experience so far, the math is balanced so that most fights are over in 3 to 5 combat rounds, as opposed to the average 10 combat rounds that most 4e encounters seemed to go, in my experience, at least. During that 3 to 5 combat rounds, the monsters are potentially capable of laying out the same or more damage vs the expected amount of opponent HP's than they were in 4e, thus making combats at least equally dangerous and most people are finding, more dangerous, than they were in 4e. The point being, decreasing the chance to hit can signifigantly increase the staying time of the monster and thus the amount of damage they can deal out, potentially completely shifting the challenge rating of encounters.