Kaido?

Please make Oni a race. PLEEEEEAAAAASSSSSE!!!!!!!!!!

So, as a fairly-new-to-5th-edition DM here, I'd like an Oni to infiltrate my party of young miscreants as a hunter or assassin for a higher power.  It's time my adventurers get started on a more epic journey of much wider proportions.  My thinking is the Oni has killed an NPC member of their party and replaced her to travel with them.  My initial question is, how long can the Oni remain in it's changed shape?  Is it until the Oni wishes it otherwise, and thus it's 24/7, or is it something that must be redone daily?

This guy is a pain to fight at level 6.

That is super cool.

Thx so much for this!

Don't yell at me this is my first time DMing a campaign. I want to make a barkeep that is an Oni in their change shape humanoid form because my players have a bad habit of starting fights first asking questions later.... what language does this monster speak?

Wait. Why is the Oni a giant? Isn't it supposed to be a fiend because of Japanese mythology portraying them as demons? Also how would they fly if they don't have the fly spell or any physical wings? I would classify them as fiends in my games, not a breed of Ogres with horns apparently. And what is the "large giant" form gonna do if its already a "large giant"? Some of this doesn't make sence. 

Quote from Redshadowblade8 >>

Wait. Why is the Oni a giant? Isn't it supposed to be a fiend because of Japanese mythology portraying them as demons? Also how would they fly if they don't have the fly spell or any physical wings? I would classify them as fiends in my games, not a breed of Ogres with horns apparently. And what is the "large giant" form gonna do if its already a "large giant"? Some of this doesn't make sence. 

 I feel like they can fly kinda like them float walking or making massive leaps like the giants from BFG, which would fit since these things are known to love eating children. Also, it can change its appearance to look like any large giant, so trolls, ogres and the like, which could be useful depending on how you use it.

Quote from katk5683 >>

Don't yell at me this is my first time DMing a campaign. I want to make a barkeep that is an Oni in their change shape humanoid form because my players have a bad habit of starting fights first asking questions later.... what language does this monster speak?

 I’m not sure if you already did it, but you can see the language section below saving throws, skills and senses. It’s common and giant

In my opinion it should tell us the “kids” rhyme from the monster manual 

Woah

Everyone's talking about the innate spell casting, but what about it's size changing feature? The stat block lists a size "large" form of the race of giants, and its "true" form separately. Yet the stat block also says that the oni is a "large" giant, so then what's its true form?

oni's are red - dnd oni is blue

they have black hair - this one has white hair

oni's have horns - no horns

oni's are like ogres - this one is like a guy you see on the street

we are not the same

.....

You actually want to play a race that eats small children as a part of their core foundational lore?!