Jak, hoping again to tap into the wand in a way that will help is finally rewarded for his efforts! He see's the invisithing take form in front of them. Blood dripping from the wounds the party has inflicted. He calls out "Get it! It's right there!" Brocc, now being able to see the invisithing moves in with his hammers. One smashes it right between the legs while the other comes down on its head. Blood exploding from both ends of the creature!

This is, of course, just going on in Jaks head. What the party see's is Jak standing waist high in water holding out the wand with a dazed look in his eyes.

That will bring us back to Brocc. ( I didn't see an edited post for int check so you can do it now)

(Back at the top with Brocc, I assume!)

(Also just realized I forgot to roll bless for my saves earlier, but thankfully I still pased'em)

Activate Nerding: 12.

For all of his bluster and frustration at the situation, there was a keen mind behind those bulbous eyes of Brocc. Even divided in focus, it still toiled -- still put together the pieces marking the characteristics of the creature for a final profile. The fact that it didn't show signs of bleeding had helped a great deal in narrowing down the list of suspects!

His eyes soon lit up with glee as he dropped his hammer just to snap his fingers. "I got you now, you insipid invisible irritant! Behold the light of truth and tremble in your enlightenment! Hoho!" He thrusts a glowing hand forth, unleashing back to back pulsing bolts in its direction. Whereas the first one wraps itself around its shape, giving it a more tangible focus point to aim, the other hammers in, further bathing it in divine light.

After each blast, a sharp yank of the hand back summons the hammer right out of the water and into his hand.

Action: Cast at 1st level Guiding Bolt at Invisithing.
To Hit: 2+11 For: 23 of radiant damage.

Adrenalin Surge: Cast at 2nd level Guiding Bolt at Invisithing(flat roll thanks to above)
To Hit: 1+26 For: 23 of radiant damage.

Bonus Action: Summon Warhammer back in hand using Bonded Weapon Feature.

Brocc finally feeling his stride, and with the help of a blessing, launches a light that illuminates the invisithing. Finally knowing where to send his weapons he lands both blows finally causing some real damage 44

In the brief time it's illuminated Brocc can see that it's not an invisible creature. It's invisible because it's the air itself manifest into form. You've heard of such things and know it's resistant to most forms of non magical attack and weapons. You also know there's no hope to grapple it, poison it,  restrain it or petrify it. It will never tire. It has a single purpose in being here. To kill you.

If Symon can see this thing well enough to touch it, he will cast Inflict Wounds, lvl 2   Attack: 15 Damage: 26

If he can not see it well enough to strike it he will cast Shield of Faith on Brocc, +2 to AC

When it is his turn of course, he is a bit more  polite than Twist.

(It's not your turn Symon and you already have 2 actions pending from last round. Please stay in initiative during combat)

The invisithing not being too happy slams into Brocc again twice.

Attack: 24 Damage: 11

Attack: 22 Damage: 13

That brings us to Johnson

(Oof. This one certainly loves to Crit. XD)

(As a reminder,, though you should probably still reckless, Jonhnson's first attack will be at advantage)

Conc. Save[DC 10]: 22.

Brocc takes the blow in stride. And though he looked bruised and battered like a boxer that just went ten rounds with a raining champ, he snorts out a glob of blood and stood his ground. "It be a creature of air, boyos! And it won't stop till I'm dead!" He warns, but with a bit of a chuckle.

After seeing Brocc taking hit after hit Johnson goes over to Brocc and says, Here, take this. And in his outstretched hand he holds a Potion of Greater Healing. 

(Johnson, anyone can take a free interact with object as part of an action (this is most used for drawing a weapon) so you can hand that off and still take an action as normal.)

After handing the potion to Brocc, Johnson rushes in to attack.

Action w/ extra attack and reckless attack & frenzy.

Attack: 19 Damage: 14

Attack: 13 Damage: 12

Attack: 17 Damage: 8

(Let's go, another crit)

Johnson still being a whirling dervish is finally repaid for his efforts as he feels all his attacks land. Again, they don't cause the expected damage but still a good chunk at 23dmg

You're even rewarding with seeing a disturbance in the water as if a wind had suddenly blown down on the spot you hit.

That brings us to Symon. Of those proposed I'd say the +2 ac to Brocc would be the most benefit. You'd have to roll a disadvantage roll for the touch spell.

A shimmering field appears around Brocc.

That will brings us to Jak

(I'll be moving for Jak in a bit. Sorry for the delay. I was trying to give Jak some time and then had a really busy weekend. I'll be able to post this afternoon, or later this morning)

Jak seeing that some hits are finally landing on this thing takes a shot with his bow.

Attack: 15 Damage: 4

Jak does land the hit as the arrows slows briefly before falling t the floor causing 2dmg

That bring us back t the top with Brocc

"My word! You can certainly take a beating can't you! Haha! But not to worry! We shall see to your dispelling post haste! Or my name isn't Brocc Brimblebacc!" Brocc declared with such conviction and passion that Oghma appeared to have heard him, because wounds start to heal and scab over within seconds. "Now watch as I spit hot fire that will drop this lousy lyre, yo!" He said, dancing a bit on the spot as he dropped the warhammer again to loose yet another bolt.

Bonus Action: Cast Healing Word at 2nd level on Brocc for 7 HP regained.

Action: Cast Fire bolt at Invisithing.
To Hit: 2+16 For: 15 of Fire damage.
(-6 damage. Forgot to remove the bonus)

Broccs words hold true as the firebolt hits the invisithing and for a brief moment you see something that looks smoke unraveling and dissipating as the invisithing DIES.

That drops us out of initiative. Good job guys! I was seriously worried for a minute there! lol

Brocc dusts his hands off as if it were no big thing. Or at least, he started to, before nearly doubling over with hand at his back. "Oh that took a lot more out of me than I thought." He grunts, and pops something back into place in his back. "Ah.. that aughta do it. Mn, yes, yes indeed. Nothing a little rest won't fix. But if you don't mind, Johnson, I will keep a hold of this for now." He gestures to the potion passed along before.

"As much as I'd like to think otherwise, we might not be so fortunate to find more here. *sniffle* Now! Where were we? Oh yes! This way, young'uns!" Brocc says as he at least started bustling down the path, taking the next right as soon as possible. Along the way he'd throw back a quick "Mind your step" and a "And thank you for the healing, by the way!" to the others without really missing a beat.

Passing the passageway that goes off to the left, you go to the end and take the right. It extends on just out of your range of vision in the dim light but after a few moments of slogging through the water you see the tunnels end. Rising from the water is a short flight of steps that ends at a closed door. 

Without missing a beat, Brocc raises one foot up high as if to take the first step. But then the paranoid kicks in. What if this was another mimic of some kind? They've already faced an air mimic. And then there was the giant human cat mimic. Maybe this whole lair was a mimic! What if--He suddenly slaps in the face. Not hard enough to do harm, but certainly enough to shock the gnome out of a terrible line of thinking!

"Get it together, Brocc! You're starting to jump at ghosts, which is a most terrible thing to do in this time you old fool." He takes a deep breathe, pats both cheeks this time, and with a final word of "Allon-sy!" he... stares at the stairs really hard for any signs of traps or mimcry afoot! Once secure in the knowledge of relative safety with the added guidance of Oghma, only then did he start hop his way on up to the door. At the top he turns and waves them on after him. Or more accurately, he points to the two elven blooded fellows and stage whispers, "Come on you two. Hope to it. This door won't listen to itself, after all. And while certainly would, uh... I forgot my hearing horn at home. Mn, yes, that's it."

Check the Stairs: 14.

The stairs seem normal stone stairs. They are damp with moss and algae growing in the cracks but are safe enough to walk on. The door shows similar signs of being exposed to moisture. The woods is swelled and algae covered near the bottom. It has a simple iron handle that is rusted but looks functional. You see no keyhole or locking mechanism from this side.

Twist comes up next to Brocc, "Le' me check thet th're door, sees ifn thar bes a trap 'r foive, eh!  Loik as nae, thet ud bes the one t' catch ye. Heh, heh, 'n wes be rather not lossin' ye Master Brocc as ye kin foight wit' an attitude; which bes a goo thin' anytoime."

He will carefully check the door and frame for any sign of a nasty trap, or five.   Investigation  18   Perception  25

(Just a heads up, in the future if you're not sure what skill to use just roll a straight d20 and tell me what you're trying to do. I'll add in the modifier. You don't have to make 2 rolls. Unless you're intentionally checking 2 different things)

Twist gets up to the door and gives it a thorough inspection for traps. He doesn't see any. The only thing he notices is that the door will be difficult to open because of the swelling of the wood, but if there are any traps they are very well hidden.