Can the tarrasque throw big things at attackers, and what would be reasonable for the damage?

Question

The tarrasque has numerous attacks: bite, claw, etc., etc. None of the stated attacks involve throwing actions, but is it reasonable that the tarrasque could throw a big thing (for instance, a bus,¹ or maybe a 1-ton rock) at an attacker? And what would be reasonable for the damage? Strictly by RAW, no throwing things attack is described, but it does not seem like an unreasonable action.

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^{1. I'm picturing your basic city transit bus, but if it makes you feel better feel free to picture a steampunk bus or a medieval wagon or an enchanted slab of rock with chairs on it pulled by pixie day-laborers. Or a flintstone's style prehistoric rock bus. Or a rock the size of a bus. :)}

Answer 1

Yes: It's an improvised weapon

Player's Handbook, p.147-148:

Sometimes characters don't have their weapons and have to attack with something whatever is close at hand. An improvised weapon include any object you can wield in one or two hands, such as broken glass, a table leg, a frying pan, a wagon wheel, or a dead goblin.

A tarrasque can wield a very large thing in one or two hands. Technically, it deals damage as a weapon which it is similar to. The core rules don't include a boulder or a bus, but the huge stone giant (Monster Manual p.156) has a rock which deals 4d10 + Strength modifier damage; the even huger storm giant's rock deals 4d12 + Strength, so we might readily assume the gargantuan tarrasque's improvised boulder would deal at least this much damage.

The drawbacks for the tarrasque are that it may not necessarily be proficient in boulders, and its Multiattack feature doesn't include boulder throws, so it won't deal the same damage per round with ranged weapons as it would melee weapons. That said, I thoroughly approve of the tarrasque taking out some of those pesky elite flying archers who aren't expecting to be struck by a castle today.