I thought I'd written this somewhere but it would appear not, anyone who gets initiative of 13 or more can act in the second round before the sentry, so fell free to take your round 2 action.
As the Monk and the squire took Julian downstairs, the party waited a moment then sprang on the sentry. Duran infuses his staff with magical power, but swings wide. Ilvillious in an attempt to ensure the Knight wasn't killed accidentally also swung wide, but managed a light blow on the knights shoulder moments before Erol shot an arrow into his knee causing him to stumble.
Before he'd had a chance to react. Illvelious made two quick follow up attacks, but they sailed through the air above the knight as he dropped to one knee. Duran also took a quick second swing but to no effect. Errol closed with him and got an arm around the knights head and face, holding him firm and blocking any chance to scream.
With blows raining near him the sentry realised he was in trouble, he fought to free himself from Erol's grip, hoping to call for help if nothing else
He was a slippery one, Ilvellios' begrudgingly admitted to himself, as he tried to connect with the sentry. Once Errol had a firm hold, he spun his staff in a swift low circle designed to have his target singing in a higher octave.
Then he swiftly brought the staff back and used it for balance as he brought his knee up into the same location.
OOC:
[roll0]
[roll1]
Bonus action:
[roll2]
[roll3]
[sblock]Ilvellios hp 21/21
Str +0(+2 Saves), Dex +3(+5 Saves), Con +1, Int +0, Wis +2, Cha -1
Acrobatics +5, Survival +5, Stealth +5, Insight +5, Perception +5
AC 16
Inspiration no
Ki: 3/3
HD: 3/3
Quarterstaff +5, 1d8+3
Unarmed/Radiant Bolt +5, 1d4+3
Given the amount of blows that have missed the guard Duran can't help but think his is protected by some divine source as he brings his stave in for a swift jab to the cut.
“Just go down, man. It will be easier on you,” Errol told the guard. He jammed his knee into the back of the guard’s knee, trying to send him to the ground.
Ilvelious and Duran both land solid blows on the knight. Under Erol's weight the knight sags to the ground. It's only after a seconds struggle with the man that Erol realises he's unconscious.
Quickly the three of you bind and gag him, checking that he is still breathing.