So the way I understand it, each missile forces a separate concentration check?

@LolChocobo Jeremy Crawford did make a tweet saying (for some stupid reason) that each missile would require a separate concentration check. 

As a DM I 100% disagree on two notions:

1. magic missile says that "darts all strike simultaneously, and you can direct them to hit one creature or several". With that and the duration being instantaneous, all damage should by definition happen all at the same time. So lets say you want all 3 darts to target a wizard concentrating on a spell. The darts don't strike on after another by the terms of how the spell is worded. you roll 3d4 + 3 and state the damage. The same would be true if you wanted 2 darts to hit the wizard and one to his familiar (or something like that), you roll 2d4 + 2 for the wizard and 1d4 + 1 for the other target and state the damage.
   
   
2. If you did allow magic missile to require separate concentration checks per dart, you're essentially allowing your players to using it as a 1st level de facto dispel magic. The intent of the spell isn't to be a counter concentration spell, but a damage spell that can split the damage to different targets. If you're using a spell way outside what the intended design is, that's a bright red flag. I personally think this issue occurs when someone reads the spell but doesn't really go into detail of what the spell is specifying. This type of issue is a reoccurring thing with spells like minor illusion and major image (using one like the other, or attempting to cause damage through them), disguise self (using it as a de facto alter self), and prestidigitation (using it out of range, trying to create an effect that would cause harm or damage to something, trying to create an effect that isn't actually listed by the spell, etc.)

I weirdly want this on a Warlock to make a Force Specialist.

Also really fun on armourer

You can only target one creature with this spell. You would need a spell like Scorching Ray to target multiple creatures.

Quote from Nookolass >>

The bigger question is that does each dart count as a separate hit? Does magic missile automatically make a downed PC fail all 3 death saving throws, as each dart is a separate source of damage?

 Yes. It also causes 3 separate concentration checks. 

One of my players got pretty scary and started using metamagic and twinned and quickened spell with magic missile (If you want full details check out my podcast, D&D Peeps)

Could a monk deflect magic missiles tho ? It’s a range attack 

I cast Magic Missile at the darkness!

Probably not. Deflect Missiles specifically says it is for ranged weapon attacks.

Quote from AshtonSurespell >>

You can only target one creature with this spell. You would need a spell like Scorching Ray to target multiple creatures.

 I don't think so. The spell specifically says that "... you can direct them to hit one creature or several."

Quote from Jared9870 >>

Since in the description, it dosnt say to make a ranged spell attack does that mean magic missile always hits?

 Yes my boi

Jeremy Crawford tweets aren't official rules, merely his opinion, unless it appears in a Sage Advice, it's not official. He's even said so in the past. If each magic missile hit caused a separate Concentration check, it would make MM an incredibly powerful tool against spellcasters, and would insta-kill downed PCs. The spell says damage is simultaneous, and that would mean to me it counts as a single damage source.

Also rolling one D4 for all the bolts is boring, much more enjoyable to roll a fist-full of D4s (and averages out the damage more).

Yes. https://youtu.be/4SAa7PmNCas

late reply, sry for that, but Arcane Firearm only works on artificer spells, anything from wands or other items don't count as "your artificer spell". Unfortunatly. 

9th level upcasting, and flavored as being green.

A sorcerer with a liking to this maneuver.

Because no one can deflect the emerald splash

Can it hit an invisible creature -- No... RAW - "Each dart hits a creature of your choice that you can *see* within range. "

It can have multiple targets by itself, even at 1st level. Therefor twinned spell isn't possible… (unfortunately)

sorry for the slow reply, hope your not dead but you can also use counterspell if you dont have shield.

Quote from Ramjet >>

Could a monk deflect magic missiles tho ? It’s a range attack 

Magic Missile is in no way, shape, or form a "ranged attack." It is a magical effect.

Note, for example, that there is no attack roll.

RAW is fun with this spell, but as soon as a player tries this level of power-gaming, i allow the monsters the same benefits. Just roll each dart separately unless you want to burn all your spell slots on spell shields or counterspells when enemy casters use MM on allies ;)