So they have their own unique language, but can’t speak them? Am I reading that right?

Edit (7/15/2022): this is basically a four year edit but please stop responding to this question. I appreciate trying to help, but I've gotten enough of the same response lol.

I guess it depends on if they are just a giant elk you encounter in the wild or if they are a summon. also they aren’t something you just encounter in a herd, they are mystical creatures. kinda makes sense for them to have their own unique “language” yknow?

Looking at other monsters with similar situations (most notably giant owls), you are correct and this particular stat block is just typed oddly. Ah well, thanks for the input!

I assume these guys are Megaceros giganteus who have fantasy-level cool antlers.

The hooves attack is almost totally useless. It can only be used on prone targets, and the only way for the Giant Elk to prone a target is through charge, which uses up its action. By the time the Elk's turn comes up again, the prone creature would have stood up again.

Unless there are... *Two* giant elk.

In all seriousness though there could be a million other situations where it would be useful. Giant Elk can be under PC control in various situations (e.g wild shape, conjure animals) and then prone could be set up by party members. Also you could design an encounter in a million different ways that has people prone without the charge.

Agreed. My barbarian grapples the targets to the ground prone and I *hooves* them. 

Elk are social animals and live in groups called herds. Herds are often quite large, with 200 or more members, according to the Smithsonian. Some herds have over 400 members. The herd is often segregated by gender, with males staying in one group and females in another. Though segregated, herds are matriarchal, which means it is run by a single female.

Harems of elk are common during mating season. A dominant male will have a herd of around six females and their yearlings. The male will defend his territory around the females until mating season is over.

Elk are most active during mornings and evenings. During the summer, elk will often migrate to higher, cooler, elevations and migrate to lower elevations in the winter.

Giant Elks only understands languages, doesnt have One 

They can speak their own, they just can't speak the other 3 after the word "understands". 

1. Make a Sage Forest Gnome Druid

2. Learn Giant Elk from your background

3. Buy a Giant Elk somehow or conjure it

4. Use your Forest Gnome powers to get a bunch of birds and whatnot

5. Ride the Giant Elk into battle with an army of birds and squirrels

6. Profit

Would this make a good mount?

Yup.

This Animal understand more languages that the average level 10 PC...

Dumbgamer99

No, they speak Giant elk and understand but don't speak common elvish and sylvan .

They have 7 Int, understand 3 languages plus have a unique language of their very own yet are unaligned? What?

Quote from Dumbgamer99 >>

So they have their own unique language, but can’t speak them? Am I reading that right?

 No, they can speak their language, but can understand (not speak) common, elvish, and sylvan.

Quote from Harrison_Sherloque_Wells >>

Quote from Dumbgamer99 >>

So they have their own unique language, but can’t speak them? Am I reading that right?

 No, they can speak their language, but can understand (not speak) common, elvish, and sylvan.

I don't see how being an experienced professional murderer lends itself to being a polyglot. If a player wants to be both they pick up the linguist feat. 

Quote from TheRoleplayer98 >>

I don't see how being an experienced professional murderer lends itself to being a polyglot. If a player wants to be both they pick up the linguist feat. 

 Alternatively, be a Half-Elf Sage to speak five languages by default.