How does variant encumbrance affect monsters like Grells?

Question

I'm running a game with variant encumbrance, and I'm wondering how the monsters would be affected. Obviously, heavily armed and armoured enemies would be hampered, but what about "drug and drag" monsters like the grell?

A grell's attack strategy is written out under its stat block, showing it to be an ambush predator (MM, p. 172):

Floating Ambushers. A grell prefers to ambush lone creatures or stragglers, hovering silently near the ceiling of a passage or cavern until a suitable target passes below, whereupon it descends quickly and wraps its tentacles around its prey. It then floats away to its lair with the paralyzed creature in its clutches.

The grell paralyzes and floats away with its prey in its tentacles:

Tentacles. Melee Weapon Attack: +4 to hit, reach 10 ft., one creature. Hit: 7 (1d10 + 2) piercing damage, and the target must succeed on a DC 11 Constitution saving throw or be poisoned for 1 minute. The poisoned target is paralyzed, and it can repeat the saving throw at the end of each of its turns, ending the effect on a success.

The target is also grappled (escape DC 15). If the target is Medium or smaller, it is also restrained until this grapple ends. While grappling the target, the grell has advantage on attack rolls against it and can’t use this attack against other targets. When the grell moves, any Medium or smaller target it is grappling moves with it.

The variant encumbrance rules state:

If you carry weight in excess of 5 times your Strength score, you are encumbered, which means your speed drops by 10 feet.

If you carry weight in excess of 10 times your Strength score, up to your maximum carrying capacity [15 times your Strength score], you are instead heavily encumbered, which means your speed drops by 20 feet and you have disadvantage on ability checks, attack rolls, and saving throws that use Strength, Dexterity, or Constitution.

The Push, Drag, or Lift rules are also important here:

You can push, drag, or lift a weight in pounds up to twice your carrying capacity (or 30 times your Strength score). While pushing or dragging weight in excess of your carrying capacity, your speed drops to 5 feet.

The grell has a fly speed of 30 ft. (hover) and a STR of 15. This means that the grell's encumbrance thresholds are 75 lbs. for being encumbered (reduced to a 20-ft. fly speed), 150 lbs. for being heavily encumbered (reduced to a 10-ft. fly speed and many other penalties), 225 lbs. for its max carrying capacity (0-ft. fly speed?), and 450 lbs. for the maximum weight it can push/drag/lift (5-ft. fly speed when above carrying capacity).

Is this right? Or am I missing a rule somewhere about hover speeds interacting with carry weight differently?

Anything larger than a frail human wizard (plus equipment) knocks its speed to 10 ft. and imposes a lot of penalties – which, while deliciously thematic and a great visual, seems like a pretty heavy nerf to the monster.

Answer 1

If you apply the rule universally, you've done the math right.

If, as the DM, you choose to apply the Variant: Encumbrance rules universally, then it seems you have done the calculus correctly and the rule heavily¹ nerfs the Grell. However, the Encumbrance rules are player facing - they appear in the Player's Handbook, and it is often the case with variant rules that they are not written with all situations in mind. In my experience, the various rule variants given in the Player's Handbook and Dungeon Master's Guide work well when applied within the immediate scope they were written for, but often fall apart when applied to other things. This is one such case.

Applying this variant rule to the Grell yields a weak creature that is inconsistent with the monster lore attested to in the Monster Manual (p. 172). The presentation there paints a picture of a monster that has no reservations when it comes to carrying off adventurer-sized prey:

[...] Grells have no compunction about attacking creatures they classify as edible, including humanoids. They tend to avoid bigger creatures that they have little hope of carrying away.

A grell will sometimes allow adventurers to wage war on the other monstrous inhabitants of the dungeon complex it calls home, staying out of the adventurers’ way as they dispose of larger threats while waiting for the right time to strike.

The idea here is that grells allow adventurers to dispose of larger threats, waiting for the adventurers to let their guard down after such threats have been neutralized. Applying the Variant: Encumbrance rules to the grell makes it so that the adventurers are the larger threats, and the result is a very different monster from the one depicted in the lore.

Ultimately, it's up to you what to do about this. Ask yourself, "what kind of threat do I want the grell to be?" If you want grells to be able to carry an adventurer away, just do that and don't worry about the calculus of encumbrance.

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^{1 Pun intended.}