[RPG] Are there creatures that are resistant/immune to falling damage

The exclusion of any mention of magical weapons isn't accidental, Barbarians are resistant to bludgeoning, piercing, and slashing damage whether it's magical or otherwise as it's key to their ability to have staying power on the front line. By comparison, the Heavy Armor Mastery feat makes the clear distinction for magic weapons, therefore, it's not unreasonable that the design intent is on purpose.

This is important because otherwise the Barbarian would experience a huge drop off in survivability as the game progressed passed a certain tier when a lot of enemies' weapons are being described as inherently magical.

The Sleep spell might work

If you are asleep, you are unconscious. If you are unconscious, you are incapacitated. (Conditions, App. A, PHB, p. 292). If you are incapacitated, you cannot concentrate.

• Being incapacitated or killed. You lose concentration on a spell if you are incapacitated or if you die. (Basic Rules, p. 80/PHB. p. 203)

The trick is to push/shove/drag the creature away from any other creature (20' or more away) if it is near other creatures (including your party), and then cast sleep at as high a level as one can.

1. One way to do that is cast a bunch of Eldritch Blasts with the Repelling Blast invocation, that hit (no damage, but target shoved or moved for each blast that hits).

2. Have your Barbarian grapple, Shove/drag/pull the target, and hope that the Barbarian has more HP than the target.

   At that point, cast sleep at as high a level as one can. Roll 5d8, and an additional 2d8 for every spell level expended above 1. Let's use a 5th level sleep to illustrate.

   Roll 5d8 + 8d8 = 13d8 which is an average of 58.5 HP. (At 7th level, 76.5).

Depending on how you roll and how much damage the target had already taken before it put up invulnerability, problem solved. If not, it was worth a try.

1. The usual caveat about not being able to put to sleep undead, or creatures immune to that condition, applies.
2. The reason that I made the estimate that the target needs to have already taken some damage is that this is a 9th level spell, so the HP of whomever is casting it is presumed to be substantial.

At higher levels, Power Word Stun

If you have access to 8th level spells, a successful Power Word Stun will incapacitate a creature. That solves the problem.

Paralysis / poison, or using a magic item, etc

Depending upon what you have available to you, anything that can inflict the paralyzed condition incapacitates the target. Various poisons can incapacitate or poison a target: Torpor(incapacitates), Essence of Ether (renders unconscious), Oil of Taggit (renders unconscious, Crawler Mucus (paralyzed). A Wand of paralysis will, if the Con save is missed, achieve that aim.

Get a Monk Involved

Even though the attack will do 0 damage, a monk attacking with Stunning Strike will stun the target. Once stunned it is incapacitated and Bob's your uncle.

PHB p. 79 (Stunning Strike)

When you hit another creature with a melee weapon attack, you can spend 1 ki point to attempt a stunning strike. The target must succeed on a Constitution saving throw, or be stunned until the end of your next turn.

I am pretty sure that a Sorcerer's Empower metamagic won't allow the HP amount to be boosted when casting the sleep spell (by re-rolling low numbers), so I asked a question about that.