It has a -2, so I'd have to roll 16 or higher...

[I haven't decided what subclass I'm going to go for with Borvnir, but if it's been shared in the campaign to unlock it, he could take the Path of the Zealot, where his god is the Undying Zombie. The more I think about it, the cooler the idea it becomes, especially with the extra necrotic damage when raging and needing no spell components for being restored to life at 3rd level and the Rage Beyond Death at 14th level, all of which are very Undyiing Zombie themed]

Zinzenzax lines up to use his desiccating breath.

Attack action, an exhalation of magical energy in a 15-foot cone. Each creature in that area must make a Dexterity saving throw DC 12.  On a failed save take 7 necrotic damage.  On a successful save take half damage.

The blast hits the two non-undying zombies, and they both are severely damaged. Irtos is up.

Finally free of the one attacking her, Irtos looks around and sees the badly damaged zombie in front of Cherry and that Cherry herself is not in great shape. So Irtos casts Healing Word on Cherry (bonus action) while casting Sacred Flame on the zombie attacking her (normal action).

Heals 9 HP

Dex 14 save to avoid 3 radiant damage

Quote from JSenecal >>

Heals 9 HP

[[ Life Domain healing is OP. :D ]]

The sacred fire sears the Great Undying Zombie, bypassing it’s necrotic life and returning it to the grave. 

Lothar rakes his claws against the zombie's arms to keep his distance. 

Att:    21

Dam: 4

Lothar Male Tabaxi Druid 7/10HP

Cherry feels renewed vigor in her from Irtos' magic and a surge of elation as the Undying One finally falls. HUZZAH! she thinks to herself. Seems her thoughts on the draconic dragon-worshipper were perhaps harsh at first. She takes her daggers and chucks them at the nearest zombie. After doing so she grabs her staff to be ready for me. But she hopes the prowress of her companions, stalwart in the face of danger, can down these undying monostrosities.

Action: Attack
Bonus Action: Two-Weapon Fighting
Object Interaction: Pick up her staff

Attack 1
To-Hit: 12+5 = 17
Damage: 2+3 = 5 piercing

Attack 2
To-Hit: 5+5 = 10
Damage: 4 piercing

Borvnir will also attack the nearest zombie with his great axe. 17 to hit, 8 damage 

The first dagger thanks into the one by Lothar, but it continues to stand until the second one strikes it between the eyes and it falls to the ground. The final zombie strikes at Zin, the blow connects with his head, and is a 21 to hit for 7 damage, *already updated* Borvnir charges in and angrily chops the zombie in half. 

Encounter over, all zombies have fallen. Out of initiative order. 

Borvnir gives a sigh of relief and sits down on the sandy shore ‘I have deep respect for those zombies’ he murmurs, ‘not only did they manage to wound me, but they were persistent, and could power through death just to continue their streak of violence. Such a trait is one I hope to emulate in future.’ He gives another flash of his horridly yellowed fangs in a grin of malice and then uses his axe to lift himself off the ground, before stretching, and then talking directly to the party ‘This island should have many more challenges in store for us. You can decide where we go next, I’ll follow behind as long as there is blood to be spilt.’ 

The Great Undying One's head rolls over and lands next to your foot and whispers, "We will see about that, dragon. We will see." 

Borvnir gives a shocked exclamation but tries to mask it as a cough (Can’t be giving away his tough guy persona after all) He then says ‘Looks like my boot got undone in that tussle, let me just sort that.’ He leans down and tries to mask his hand movements with the bulk of his body, sweeping the zombie head into his bag, and hisses very, very quietly ‘You’re a special one aren’t you? I don’t expect much from you, but I think we could maybe work out a partnership when we’re away from these other folk?’ He then ties his laces like normal and pretends he doesn’t know his left and rights to explain how long it was taking to do them up. 

Deception check into bluffing the party: NAT 20!!!!

His modifier is 0 so just 20, if anyone wants to try to beat it with insight. 

Irtos Insight 24, but since she didn't have any reason to suspect anything, perhaps passive insight of 16 would be more appropriate.

Insight: 20+1 = 21 //wow

Cherry furrows her brows with anger. She goes over to pick up her daggers and then comes up to Borvnir, shaking her staff. "You're hiding something, dragon," she says the last word as if it's a curse word, "Spit it out, boyo!"

Intimidation: 1+5 = 6
//apparently the 3' 3" halfling wasn't able to be all that intimidating to the, what, 7-8' dragonborn?
//feel free to use or disregard the roll; your choice

[[ Cherry's backstory has her town&family getting killed by a dragon, so figure she'd be a bit distrustful of dragonoid creatures. Hence her suspicion with Borvnir hiding something. But also saw him fighting well against the zombies with the group, so got that as a fallback to make sure she can still work with him regardless how this exchange goes. (Want to make sure our adventuring party stays a party after all.) ]]

'I ain't got nothing to hide, you pipsqueak' he growls. 'If you really must know I was picking up the head of that particularly hardy zombie to keep as a war trophy. I didn't want to be too open about it as it was Irtos's kill, and I didn't wanma risk him wanting it for themselves.' He turns to Irtos and says with a toothy smile 'I'm sure you've got no use for a head after all, and would be happy for me to keep it, right? Now if we're all settled over what I was doing with the head, let's move onto what we're here to accomplish'

Cherry snorts. "Hrmmph." Disgruntled by the dragonborn's response, but he had fought well during the encounter. No sense pushing the matter more right now. She turns around and walks towards Irtos. "I'm for heading into town too," she says, agreeing with Borvnir.

'Going into town sounds great, good idea, who else is up for heading there now?' Borvnir asks in a cheery tone. Even though he hates towns as they remind him of his difficult childhood, he thinks it best to try and get on good terms with Cherry again. He doesn't care if they become friends at all, just that being cordial towards her may ease some suspicion. Even better so, he might be able to break from the group at some point to find a back alley to communicate with the Great Undying One again whilst the rest of the party is busy shopping or whatever else. He's unsure what to expect from the head; perhaps it might never speak again and it used it's final burst of life to speak to him, but Borvnir knows that zombies don't usually talk, so something must be afoot. He might even gain some information to share with the party to cover up and distract them from his absence when he's gone. Either way, Borvnir isn't the brightest and definitely doesn't plan ahead, almost always going with his gut, but he feels this head may be important.