Is it possible for a PC to become Huge or larger, in order to try and grapple a Tarrasque?

Question

The way our game is going, it is entirely feasible we may end up fighting a Tarrasque.

When it comes to grappling, RAW says the following:

The target of your grapple must be no more than one size larger than you...

To my knowledge, enlarge/reduce doesn't stack with itself and that's the only means in the game to increase one's size. As that only gets you to Large, the best you can hope for is Huge creatures.

Using RAW, is it possible to increase your size one more step to at least Huge (or more) so that you can actually attempt a grapple on a Gargantuan-sized creature?

Answer 1

Yes, it is possible, Tasha's introduces the Rune Knight, and 'Giant Might' the third level feature allows you to grow to Large size, furthermore 'Runic Juggernaut' at level 18 increases that size to Huge. All you need then is an enlarge spell and you're good to go!

Yes, I know this is 2 years old (almost three) but I still wanted to respond :)

Answer 2

In addition to the other answer, Storm King's Thunder introduces us to the magic item Potion of Giant Size.

When you drink this potion, you become Huge for 24 hours if you are Medium or smaller, otherwise the potion does nothing.

Answer 3

First, become large. Then enlarge.

This questions addresses how (if) you can do it. Then just cast enlarge. This is in case you want to stay yourself.

Shapechange or similar

As Quadratic Wizard's answer states, you can shapechange (or true polymorph, or polymorph, or w/e) into something Huge, or something Large and then someone else casts Enlarge on you. He says Polymorph wouldn't work, but I'll state my case on how it might work (at least under one interpretation of the rules).

Monsters have special rules for grappling. The first is mentioned in the MM p. 11.

Many monsters have special attacks that allow them to quickly grapple prey. When a monster hits with such an attack, it doesn't need to make an additional ability check to determine whether the grapple succeeds, unless the attack says otherwise. A creature grappled by the monster can use its action to try to escape. To do so, it must succeed on a Strength (Athletics) or Dexterity (Acrobatics) check against the escape DC in the monster's stat block. If no escape DC is given, assume the DC is 10 +the monster's Strength (Athletics) modifier.

Second, creatures like the Giant Octupus can grapple, even though they have no "hands" (i.e., for them, it requires no hands). The Tarrasque itself can grapple using his jaws. TL;DR: creatures can grapple with rules different from the standard grappling from PHB - they can use their mouths, as an example.

Bite. Melee Weapon Attack: + 19 to hit, reach 10 ft., one target. Hit: 36 (4d1 2 + 10) piercing damage. If the target is a creature, it is grappled (escape DC 20). [...]

That said, let's check some beasts that can grapple. As already mentioned, the Giant Octopus can do it.

Tentacles. Melee Weapon Attack: +5 to hit, reach 15 ft., one target. Hit: 10 (2d6 + 3) bludgeoning damage. If the target is a creature, it is grappled (escape DC 16).

Note that it doesn't even state a Size restriction. Even if you want to consider it, Giant Octopus is Large and can be Enlarged to Huge, following the general rule as well as the specific rules.

If you really want to say that tentacles are hands, I'll use my mouth. Giant Toad is again a Large Beast that can grapple without using hands.

Bite. Melee Weapon Attack: +4 to hit, reach 5 ft., one target. Hit: 7 (1d10 + 2) piercing damage plus 5 (1d10) poison damage, and the target is grappled (escape DC 13).

Anyway, there are a few creatures that can grapple without using hands, and you can grapple with all of them. Other spells also don't have this limitation, so it's fine.

Wish.

Well, it wouldn't be a complete answer if "Wish" wasn't here, right?

Answer 4

In addition to the options sugggested by the other answers, Unearthed Arcana: Giant Soul Sorcerer introduces a new giant-themed sorcerer subclass. The Giant Soul Sorcerer has a 14th-level feature, Rage of Fallen Ostoria, which allows you to increase your size in certain circumstances:

Starting at 14th level, you gain the ability to channel the souls of your ancestors into your physical form. When you start casting a sorcerer spell on your turn and expend a spell slot, you can increase your size by one category — from Medium to Large, for example.

This increase lasts for 1 minute. It ends early if you die or are incapacitated.

It also grants certain other benefits for the duration, in addition to the size increase.

Answer 5

Shapechange

Shapechange or another spell or ability which works similarly can allow you to transform into another creature which may be Huge size, such as a type of giant:

You assume the form of a different creature for the duration. The new form can be of any creature with a challenge rating equal to your level or lower. The creature can't be a construct or an undead, and you must have seen the sort of creature at least once.

That spell places no restrictions on what size you can become. It's a 9th level spell, but if you're fighting the tarrasque you want to be high level anyway. It's also good for languages!