I'm looking at its stat block, and the resistances/immunities...can this thing be charmed? Perhaps convinced through the charm that they've completed their task, and then it would just fade away.

Seems like the best option for the conjure elemental spell. Cast it far away and send him off to kill your enemies. Cant loose concentration if youre a kilometer away from battle.

Quote from OrsikBattlehammerII >>

 

Quote from trapbuilder2 >>

Quote from BirdMonk >>

Could I say...

Me: "Hey Mr. Invisible Stalker, I wanna know where the evil king is."

Stalker: "He is hiding in his top secret base that nobody knows about at coordinates x, y, and z..."

Me: "Alrighty let's go"

 Only if you understand Auran

I have an Aarokora that is fluent in it, as well as a teifling warlock that knows comprehend languanges, so would that work, of say, my water genasei druid summoned it, and then asked one of my other characters to be a translator for Auran?

 (I didn't quote for the comment I have right above this text, so just pretend, ok?)

Quote from OldGrumpyBear >>

I'm looking at its stat block, and the resistances/immunities...can this thing be charmed? Perhaps convinced through the charm that they've completed their task, and then it would just fade away.

 The problem is most charm spells affect a target that you can see (actually, most single-target saving-throw spells have this limitation).

I guess not, you can only command it to kill or retrieve an item. Ask it to fetch the evil kings crown and follow it

This thing is invisible, which means these:

No opportunity attacks unless you can see it

Advantage on its attacks

Disadvantage when attacking it

You need faerie fire

Thats why it’s Cr6 despite only having 2xSlam for +6, 10 damage

If you speak Auran, but it couldn't reply because it doesn't speak.

The stat block says that it can:

Understand and Speak Auran

Understan but not speak Common

Never knew about these creatures until I read the recommended summons from the “Conjure Elemental” spell...

Makes me want to try a Conjuration Wizard.

Conjuration Wizard: “Behold! My terrifying champion!”

(they flourish their hands; and a puff of smoke faintly pops and vanishes)

Enemy: “Uh...nothing happened.”

Conjuration Wizard: “Just wait for it...you’ll figure it out.”

This thing.......just reading about it makes me imagine the horror my players would have fighting this. It is permanately invisible and it can hover, making it not detectable by sound invisible creatures make when walking on the ground. And it still remain invisible as it attacks. Unless someone in the them has blindsight or can see invisible creatures, this would be a nightmare to fight............This will be the perfect enemy for my players who wants a challenge.

Does the Invisible stalker regenerate Hit points? and how can players attack it?

Question,  Can a Bard (if he/she haven't learned Faerie Fire) use his/hers "See Invisibility"  spell to locate this Elemental invisible stalker?

Ps. i am a beginning Dm, is a elemental somewhat the same as a Ethereal creature?

Got me thinking: what about hitting it with arrows? Would the arrows stuck, giving away its position, or would they just pass through it?

Yes.

No, "Ethereal" is not a creature type, as Elementals are, but things like Ghosts traverse the Ethereal Plane. In the same way, if you were in the Astral sea that wouldn't make you an "Astral" creature.

Let me get this straight, this thing is completely invisible, knows exactly where you are at all times and doesn’t need to eat or sleep so it will always be coming after you and it’s resistant to non-magical weapons!

And this thing can move 100 feet (50 + 50 fly) if it wants AND attack?

So it can sweep in at a range from 50 feet, attack twice, move away 50 feet without getting an opportunity attack against it. 

You can argue that the walkspeed of 50 would reveal it's location by swirling wind across the floor, but if he uses that to approach and fly away 50 feet the party wouldn't know where it is and it could repeat that every time... Making it hard to kill, throwing fireballs or other AOE attacks at random might be the only thing working at that stage if they don't have access to seeing invisible creatures... This is going to be fun!

no, that is not how movement speeds work.

Consider reading : https://www.dndbeyond.com/sources/basic-rules/combat#BreakingUpYourMove

What kind of NPC (statblock) would be able to summon such a creature?

Quote from ElRomero >>

I have dated a few of these in the past. Scary.

 run.

Who is that guy inside the stalker? Is the stalker attacking it, is it part of the stalker, or is the stalker moving it with its air? If the stalker is attacking it, does that mean the stalker can occupy a creature's space when attacking it and/or move the creature with itself?  Also, on the image you see rocks and leaves flying, does that mean the stalker moves light objects when it walks or hovers?