How tall would a Giant Ape be, on average? I mean, if it can leap 30 feet, and has a 10 foot reach, what is the maximum height a flying creature can be before it leaves melee range? Would it be fair to assume the Giant Ape would be about 20 feet tall? And can therefore reach a flying creature who is 55-60 feet in the air?

Also, not sure how I feel about the only ranged attack the Giant Ape had now being a rechargeable ability. Wondering if there is some middle ground between "rechargeable, multi-target, always deals damage", and "single-target, hit or miss, but can use it every turn if needed".

The Boulder Toss is quite strong though; it got buffed from a 50ft normal range to 90ft and the half damage on succesful save + prone on fail is quite a terrifying combination. And to be fair, with the Leap BA he gets up to 60ft of movement per turn so he'll be jumping all around the map throwing punches 84% of the time.

I'd say a minimum of 15 feet

Quote from Vardaemir >>

The Boulder Toss is quite strong though; it got buffed from a 50ft normal range to 90ft and the half damage on succesful save + prone on fail is quite a terrifying combination. And to be fair, with the Leap BA he gets up to 60ft of movement per turn so he'll be jumping all around the map throwing punches 84% of the time.

Yeah, it is a strong ability, and the BA Leap does make for a very "cinematic", though potentially very short (because of Attacks of Opportunity), fight. But, I just feel like not being able to throw a boulder when you really want or need to throw a boulder is something that might be missed. The more I think of it, the more I think "Boulder Toss" can be this big, massive, rechargeable attack as written, but I might also add back in the Rock attack from 2014, just with less damage and still a single target. Best of both worlds that way.

who would win 100 humanoids or one giant ape 

Giant ape 100%  😭

If the humanoids are the worst possible option (commoners) it’s closer than one might think. I mean with a +2 each one has a 50/50 chance to hit averaging 2 damage, if they get initiative about half of them can hit and deal 50 damage in the first round at least. I mean crowding would be an issue but they could all back up to let others in, after all the giant ape only has one reaction.

It amuses me greatly that you gave a serious answer to this question.

ha nerd

jk I would think the same

Not to be nit-picky, but isn't it further in the side of the commoners as they actually have a 55% chance of hitting him, as they only need to roll a 10 or higher due to the +2 bonus they get.  1-9: 9 possibilities of failure. 10-20: 11 possibilities of success.

Though granted, if we assume the giant ape rolls an average initiative number of around 10-11 (15-16 because of the bonus), it would likely go before more than half the commoners due to the ape's +5 initiative bonus over the +0 of the commoner.

Can larger monsters hit more than more commoner at a time with an attack. The fist looks like it would easily squash two clumped together commoners, and the "one target" line is removed in the new MM, but I assume the game works the same as it did before. If the ape cannot punch multiple commoner's to death at a time, then the commoner's will win eventually as even if the giant ape hit all its attacks, it would only be able to get rid of 2 of them at time, giving them around 50 turns (meaning they would only need to do 3-4 damage per turn to win which can be done with only 1-2 commoners hitting it each turn or even one commoner that rolls very well each round), unless the ape uses boulders to kill multiple commoner's with its AOE damage (combined with its greater movement than the commoners and the range capabilities of the boulder, it does seem to be the infinitely better choice unless this ape is more stubborn than intelligent).

Wouldn't the ape, with its greater movement, just kite and fist? Every sixth round boulder toss? Also, bonus action leap.

The ape would win, hands down. It would be a slaughter. 

It would be at least >16 feet tall if not larger since its Huge in size, but in the end of the day it's up to the DM to decide how tall it truly is. I'd say anything above 28 feet is too tall, so a nice average of about 22 feet would be how tall I'd rule it.