You couldn't before, but in the D&D 2024 Player's Handbook you can stack friendly creatures in the same space

The Dungeons & Dragons 2024 Player's Handbook is less than a month away, hitting store shelves on September 17. Changes are coming. Some changes are big. But some amount to nothing more than moving the furniture around. Such as this next bit:

You'll soon be able to stack allied creatures in the same square. You couldn't do that before.

Yes, you could move through a nonhostile creature's square in D&D 5e, but it's treated as Difficult Terrain, meaning it doubles your movement cost to do so. Moving through the five-foot square of a nonhostile creature's space costs you 10 feet of movement. But you absolutely, positively can't end your turn in another creature's space. The PHB doesn't say what happens if you try. It just says you can't. 

But in the 2024 Player's Handbook you can. You simply receive the Prone condition to do so. You're now on the floor with your ally standing over you. I imagine it looks something like PSY and the Elevator Guy in the "Gangnam Style" music video.

Going Prone is not always a bad thing in D&D. It's sometimes a useful tactic, depending on your enemies' placement on the board. If they can run up adjacent to you and perform a melee attack, that's bad for you. You being Prone means they'll attack you with Advantage (rolling two dice instead of one and keeping the higher result). But if your enemies are further than five feet away, you being Prone means they attack you with Disadvantage (rolling two dice instead of one and keeping the lower result). 

Got some enemies firing on you with missile weapons from a distance? Being Prone is excellent because you've effectively just made yourself a smaller target as they attack with Disadvantage. But, vice versa, watch out if you're prone and enemies can run up on you.

Also, attacking from a Prone position gives you Disadvantage on your attack roll. Perhaps you use the 2024 PHB's Heroic Inspiration to give you Advantage and turn that Disadvantage into a normal attack roll. Feels like a waste, but it may be just the miracle you need in the moment. 

Not only can you stack allied creatures in the same space, but it's no longer considered Difficult Terrain to move through an ally's square. Your ally politely sidesteps you running through their square. They'll bow with a flourish and a "m'lord/m'lady" if they know what's good for them, too.