"Invisible?!" Grugga shouts back, perplexed. He changes to Elvish and yells at Zip, "Zip, 30 ft up, get a look in those ferns. Maintain altitude over any threat you recognize." Grugga then falls in with Kurt and takes the dodge action.

Edit:
Perception from Zip: 21

Zip must be able to hear but I doubt it can smell.

Rohuzar and Cliff advance as quietly as they can toward the mound with the campfire and Kiteborne likewise approaches slowly from the south.  

Guilim draws his polearm and watches for a sign of where their quarry may be hiding, while Leelan slips into the tall ferns and seems to vanish.

In that moment, the silence is broken.  "It's here, it's invisible, fall back!" Aubrey shouts on the top of his lungs, almost in panic, and he breaks into a sprint at supernatural speed, circling the mound along the east side.  Grugga calls out to Zip in Elvish and the little homunculus flies upward... and comes to rest just above Kurt, who stares at it with dread....

17

15

What happens next happens fast.  Kurt grimaces with shock and seems to float off the ground... and then the air shimmers and distorts, revealing a 10 foot tall, robust and dirty humanoid - an Ogre!  It is clad in a hide jerkin with a deer skin cloak.  Kurt the halfling is clutched in its left hand; the other hand is holding some sort of round stone disc.

The Ogre growls in Giant:

 Initiative:

Morbo:  15

Grugga:  6

Aubrey:  22

Guilim:  2

Leelan:  20

Rohuzar:  11

Cliff/Kurt/Kiteborne (shared initiative):  21

*For those on the opposite side of the hill from the Ogre, the Ogre currently has 1/2 cover.*

Seeing Kurt captured Aubrey moves back (to get within 60 ft) and then calls upon the power of his talisman and whispers a discordant melody wracking the ogre with terrible pain.

(Dissonant Whispers Save Wis 13 or 13 psychic damage and must immediately use its reaction, if available, to move as far as its speed allows away from you. On a successful save, the target takes half as much damage and doesn’t have to move away.)

If unsuccessful Aubrey then uses the rest of his movement to find cover on the south side of the hill.

Mordo WIS save for Dissonant Whispers: 4

 The Ogre grimaces at an unseen source of pain and turns and locks eyes with Aubrey... but then backs away 20ft into the dense ferns to its west.  Aubrey, seeing his spell take effect, stands his ground to the northeast side of the hill.  (Right?  Your post said you retreated south 'if unsuccessful".)

"Shite!  Kurt!"  Cliff springs into action alongside Rohuzar and dashes to the northeast toward the ogre holding his partner, though he cannot get into melee range this turn.

Unable to see Kurt, but seeing the Ogre's massive form over the hill, Kiteborne races down the path and up the hill to get a better look... and get within range of spells for next turn.

Kurt, swinging back and forth as the Ogre carries him in its outstretched left hand, is screaming in panic.  He slashes at the Ogre's closed fist around him with a dagger.  Attack: 13 Damage: 6  Blood is drawn, but rather than drop him, the Ogre looks down at the small figure in his hand with burning contempt.

(Leelan is up!  Then the Ogre!)

(Yes, Aubrey stands his ground :-)

Hiding in the southern patch of ferns, Leelan watches in horror as the ogre gets the jump on Kurt. He move 10 feet north through the rough terrain (1 hex northeast, 1 hex north).

Popping out of hiding, he will release an arrow at the brutish creature. But beforehand, the gnome will imbue the arrow with a bit of magic as small bramble start to grow around the shaft of the arrow.

Bonus action: cast ensnaring strike On a hit: strength saving throw dc 11 (with advantage because it’s a large creature) or be restrained

Takes 1d6 piercing damage at the start of its turn if restrained. Can use an action to make Strength check to break free.

Action: Attack: 10 Damage: 4

 From deep in the thick ferns to the south, an arrow flies.  The Ogre, still staring down at the pesky halfling in his hand, is caught unawares and it lodges in the thick muscles just below its neck.  The beast throws its head back and howls, nearly shaking the ground, and its cry reverberates through your ears.

Morbo STR save:  20

Vines begin to sprout from the arrow and weave around the Ogre's neck and upper arm... But with another bellow of pain it reaches back and - using hapless Kurt - brushes the arrow and vines away.

It wheels, then, looking for its hidden tormentor, but before it sees only Cliff, who had been racing to Kurt's aid.  Now, Cliff skids to a stop as the ogre turns on him.  Tearing thick ferns out with its huge feet as it walks, it strides to Cliff and then strikes out at him twice, using Kurt like a club and swinging down violently.  (On a hit, damage is split 50/50 between Kurt and target.  On a miss, full damage is taken by Kurt as he is slammed into the ground.)

Slam 1:   Attack: 25 Damage: 10

Slam 2:  Attack: 20 Damage: 15

 The first attack catches Cliff by surprise and Kurt is smashed down upon him like a hammer and nail.  Whipped back up for another attack, you can make out the bloodied halfling's cry, "I blame you, Cliff!"  The first attack knocked Cliff back slightly, and the Ogre's second attack slams poor Kurt into the forest floor.  When the Ogre lifts his hand again, Kurt is now hanging limp and lifelessly....

 (Rohuzar, Grugga, Guilim, and then Aubrey are up in that order... if you want to post sooner or out of order go ahead but I will try to process the events in proper order in summary)

Since he knows that he can not get close enough to attack, Guilim will move his normal 25 feet and then take the Dodge Action incase the ogre suddenly turns on him suddenly.

Grugga sends Zip in to deliver Cure Wounds Healing: 4. ((Zip can fly 30 ft; should be within range. Delivering my touch spell is Zip's reaction.)) Grugga takes his healing box out, opens it up, and drops a small gem the color of Zip's pearl inside. He grinds away at the crank, and instead of healing mist coming out of his box, it blows out of Zip's pearl and onto Kurt's badly wounded body.

Grugga then commands Zip to take evasive action (dodge).

He yells at Cliff, "Pull him out of there!"

Rohuzar runs forward and swipes with his battleaxe at the hand holding Kurt. 

Attack: 21 Damage: 5 

using DM inspiration on the attack 13 

Aubrey repositions a bit to get a clear shot on the ogre, still keeping his distance, and then he uses the powers of his talisman to send a golden beam of crackling force towards the ogre.

Eldritch blast: 9 Damage: 11

Also using inspiration if allowed: 22

Rohuzar charges the Ogre and swings for the hand holding Kurt... but as he adjusts his swing so as not to hit the unconscious halfling, the Ogre is able to take advantage and pull his hand out of the strike zone, and Rohuzar's swings meets empty air.

Grugga makes use of his mechanical pet to administer a healing spell to Kurt.  Mists pour from the hovering Zip.  There is an audible 'pop' as the halfling's dislocated jaw pops back into place and some of his head wounds close and cease their bleeding.  His eyes open wide, and he cries out in horror as he sees he is still in the Ogre's grasp.  Grugga yells at Cliff, "Pull him out of there!" and Zip begins dancing back and forth around the Ogre.

Guilim chugs forward toward the carnage, halberd raised to ward off any attacks.

(end Round One)

Aubrey repositions a bit to get a clear shot on the ogre, still keeping his distance, and then he uses the powers of his talisman to send a golden beam of crackling force towards the Ogre.  He feels his attack going just wide, but wills (inspiration) it back on target, and the energy rakes across the monster's back.

The Ogre looks as though it is cocking back to throw Kurt at Aubrey in response to that last magical attack.  Cliff takes the opportunity to try to free Kurt from the creature's fist.

Kurt's acrobatics check to escape the grapple (w/advantage from the help):  17

Morbo check to hold on:  23

And with help from Cliff, Kurt is able to wriggle out of the Ogre's grasp and lands on his feet!

Kiteborne advances closes atop the hill.  He draws his birdpipes and plays a few notes, then tells a joke.  "Say, creature?  Did you hear the one about the oversized brute who wasn't housebroken?  They say he pissed all ogre the floor."

Morbo WIS save: 4

But the Ogre completely ignores the elf, instead focused on the Orc, Human, Halfling and tiny robot screw surrounding him.

(Leelan is up!  Then the Ogre!)

Leelan can’t help but chuckle a bit at Kiteborne’s joke.

With the halfling now freed from the Ogre’s grasp, Leelan will close in with the rest of the group on the big fat bully. (25 feet forward)

He will then release another arrow, hoping to have the same result as the previous one.

Attack: 22 Damage: 8

Another arrow sails from across the field, finding soft tissue in the Ogre's shoulder.  It shudders and growls, then it wheels again looking in vain for its small, distant tormentor. 

Now surrounded, it looks at its empty hand and then smiles.  "Morbo strong," it barks out in the common tongue.  It tosses the stone disc in its right hand up in the air and then stretched out its arms and brings them together in a thunderous clap.  There is an explosion of sound and the shock wave rips across the clearing, uprooting small plants and stripping leaves from a nearby tree.  Rohuzar, Cliff, Kurt and Zip must make STR saves DC 12.   On a failed save they each take 14 thunder damage and are pushed 10 feet away from the Ogre.  On a successful save they take half damage and are not moved.

Cliff STR save:  6

Kurt STR save:  2

Zip STR save:  14

Kurt, still dazed from his prior injuries, is caught of guard.  The blast throws him 10ft backward and he lands in a heap, disappearing into the thick ferns.  He does not rise.  Zip holds firm against the blast, but the little machine's strength is greater than its construction, as tiny pieces flake away in the force of the blast until only the pearl remains, before it falls to the ground on the north side of the hill.  Cliff braces himself and withstands the concussive blast, though he's bleeding as if from a broken nose.  He slashes at the heels of the Ogre as it flees up the hill (AoO):  Attack: 12 Damage: 11

The Ogre catches the stone disc on its way back down and then strides up the hill and stands beside some rubble of the old structure, towering over Kiteborne.  Standing at the highest point in the clearing, it bellows again in common, "MORBO STRONG!!"

(Any of Cliff, Kurt and Rohuzar who make the save and aren't pushed away (and are still conscious) can take an Attack of Opportunity against the Ogre as it disengages.)

(This map assumed Rohuzar makes his save.  If he fails, he should be 2 hexes to the southwest.  Rohuzar, Grugga, Guilim are up... then Aubrey to start round 3!)

Grugga curses the ogre. He pulls out a purple crystal with the clockwork "mallet" looped around it, cocks the mallet, and lobs it in an arc over Morbo's head. He attempts to cast Faerie Fire on him. ((20ft cube. Can I cast it without hitting an ally?))

Grugga then runs over to Kurt in the bushes and stands over him, ready to protect him.

Morbo DEX save:  16

A shower of tiny pink and purple dust particles rain down above the Ogre, leaving it twinkling and sparkling.  It looks at the colors and laughs, perhaps not aware that attack rolls now have advantage against it. 

Guilim will move his full movement to get near the fire and so he can better see the ogre. As he stops he slams the butt of his halberd into the ground and then casts Command on the ogre. "Fall!"

Needs to make. DC 13 Wis save.