Do monster races and player races have separate functions for a reason?

I’m trying to understand if player races and monster races with the same abilities function differently. I had this issue arise with player regarding a monster race and a player race not having the same ability.

In the MM pg. 122, the Duergar monster race has this ability:

Enlarge (Recharges after a Short or Long Rest). For 1 minute, the duergar magically increases in size, along with anything it is wearing or carrying. While enlarged, the duergar is Large, doubles its damage dice on Strength-based weapon attacks (included in the attacks), and makes Strength checks and Strength saving throws with advantage. If the duergar lacks the room to become Large, it attains the maximum size possible in the space available.

While in the SCAG, the Duergar player subrace have this ability:

Duergar Magic. When you reach 3rd level, you can cast the enlarge/reduce spell on yourself once with this trait, using only the spell’s enlarge option. When you reach 5th level, you can cast the invisibility spell on yourself once with this trait. You don’t need material components for either spell, and you can’t cast them while you’re in direct sunlight, although sunlight has no effect on them once cast. You regain the ability to cast these spells with this trait when you finish a long rest. Intelligence is your spellcasting ability for these spells.

The issue that arose is that a player who is playing a duergar and used enlarge on himself had to keep rolling for concentration when attacked, but the duergar monster that was also enlarged whom he was fighting did not.

My question is why does a monster race and a player race have two different abilities? Shouldn’t they be the same?

Does enlarge for a duergar monster function the same as a duergar player race? [duplicate]

This question already has an answer here:

  • Does a duergar NPC need to concentrate to maintain its Enlarge ability? 1 answer

I’m trying to make a DM ruling on this and it’s kinda hard. In the MM, the duergar monster can use the abilities Enlarge and Invisibility as racial abilities that do not require concentration or act like spells to be countered; however, the Duergar subrace in SCAG states that you can cast enlarge/reduce or invisibility on yourself as a spell and requires concentration.

The issue that arose is that a player who is playing a duergar and used enlarge on himself had to keep rolling for concentration when attacked, but the duergar monster that was also enlarged he was fighting did not.

My question is would the subrace act as the monster does (i.e. not requiring concentration to stay enlarged) or would the monster act as the subrace does (i.e. requiring concentration to stay enlarged)? Or are they separate entirely because of a balance mechanic between monster and player?

Can you take the average damage roll when changed into a Monster?

In this answer the idea of PCs using the following quote from the Monster Manual came up:

Any damage dealt or other effects that occur as a result of an attack hitting a target are described after the “Hit” notation. You have the option of taking average damage or rolling the damage; for this reason, both the average damage and the die expression are presented.

I’m wondering whether this rule only applies to monsters or if PCs who have used Wild Shape or similar things to become monsters can also use this.

Can a surprised monster use lair actions if they roll high initiative?

The rules for lair actions say:

On initiative count 20 (losing all initiative ties), it can use one of its lair action options. It can’t do so while incapacitated or otherwise unable to take actions. If surprised, it can’t use one until after its first turn in the combat.

If a creature with lair actions is surprised but rolls a 21+ on initiative, can it use a lair action on the first round? By the time initiative count 20 occurs, the surprised creature has already had a turn that combat (which it spent being surprised).

What “level” is a monster, for the Tough feat?

It seems that if a couatl changes shape into a humanoid, it can get racial features. But if it decides to turn into a variant human and picks the Tough feat, is its level its CR (4) or its number of hit dice (13)? What if it changes into a mage that specifies it’s an “x-level spellcaster”? (I know it wouldn’t get spellcasting, but if this feat would normally be unavailable for creatures without levels, would doing this give it a usable level?)

This actually probably applies in exactly the same way to the less-complicated situation of “NPC humanoid, what’s its level?” but maybe it’s different?

Monster with resistance to bludgeoning and fire damage from nonmagical weapons have resistance to a warhammer’s bludgeoning but not its fire damage?

My friend has an enchanted silvered warhammer that grants it +1d6 fire damage. We’ll be fighting a fiend soon with resistance to fire and bludgeoning damage from nonmagical and non silvered weapons.

My friend’s warhammer makes half bludgeoning damage and full fire damage to the fiend?

Taking levels in monster types

Today I found this post on reddit and in one of the comments they mention taking levels in fey, outsider, and aberration (not all at the same time). Are there any alternate rules I’m not aware of or are they just referring to monsters as pcs rules from the srd.

Heres the OP

Over the past few days with some help from members of the /r/touhou Skype group, I have made a spreadsheet listing (almost) every Touhou character and have filled in some slots slots along their names accounting for their D&D Morality Alignment, Four Temperaments, MBTI, and other silly things that aren’t as relevant.

Chart (not very complete):

D&D Alignments explained:

Four Temperaments explained:

MBTI is harder to grasp, especially the cognitive functions but there are more than enough online resources detailing that.

Enneagram explained:

If there is anything that should be put in or whatnot, please leave your thoughts on characters and also your alignment/MBTI/other if you like.

EDIT: If I like a suggestion and want to add it, I’ll do so in the name of the user who suggested it. You can also leave comments on the sheet as well.

Here’s an excerpt

Now, let’s see. You’ve given D&D (presumably 3.5e rather than 4e or 5e) classes and Pathfinder classes as a category. I can definitely help with that. Going down the line:

Rumia probably doesn’t have class levels, but she’d be a Commoner or just take levels of Outsider(Edit: Or Aberration, depending on how you see Youkai) if she did.

Letty Whiterock is probably just a Fey.

Kogasa Tatara is just an Aberration with Aberration levels.

Can a monster take the Dodge action without the PC knowing prior to attacking?

Consider the following scenario: On its turn, a monster uses some movement and ends its turn without taking an obvious Action. Secretly, it has taken the Dodge action. On the player’s turn, the player attacks the monster. The DM instructs the player to roll with disadvantage, as the monster is dodging. The player might not have chosen to attack that monster if s/he had known it was dodging. (Of course, an observant player might deduce that the monster is dodging, as it took no obvious Action.)

Is this a legitimate tactic for the DM to use? Or should a PC be able to detect that a target is dodging before deciding to attack?

If a monster escapes my grapple, can it immediately move away?

A grappled creature had 0 speed, so it can’t get away from me. But it can attempt to escape the grapple as an action.

If it attempts to escape and succeeds, does it immediately get its speed back, and is therefore able to move away in the same round? Or is it not able to move away the same round it escapes because it began its turn with 0 speed?