Ambiguous Situation: Brain and Climb wonder why Gazef challenged Ainz to a duel. Climb thinks that Gazef was trying to help them find a weakness in Ainz. Of course, this is a very optimistic perspective and Gazef may have had other reasons for why he did it.
The Bad Guy Wins: Ainz and Nazarick successfully take over E-Rantel and crippled Re-Estize's entire military force.
Blackmail: Ainz arranges Momon to be his enforcer for E-Rantel otherwise he'll have his forces wipe out the entire city. Momon agrees but makes it clear that should he hear the slightest grievance from the people, he'll have Ainz's head.
Despair Event Horizon: King Ramposa, Brain and Climb are certainly in deep sadness after Gazef is killed.
Climb lies to Renner about the true scope of Nazarick's power to ensure she never loses hope. Unfortunately, Renner does know and is one of Nazarick's conspirators.
The people of E-Rantel would rather stay with Momon than Re-Estize to protect them from Ainz Ooal Gown. Unknown to them, Momon is Ainz.
Engineered Heroics: Nazarick does this at the end, painting Momon as E-Rantel's true hero. That's because Momon is Ainz Ooal Gown and their true plan is to make the denizens of the city more loyal to him than to the kingdom.
Et Tu, Brute?: To all of E-Rantel's horror, Re-Estize chose to abandon them to Nazarick.
Heroic BSoD: Brain, Climb and Ramposa goes through this after Gazef died.
Heroic Sacrifice: Climb believes Gazef's actions to be this, hoping they could find some weakness in Ainz.
Heroic Vow: After getting comfort from Climb, Brain unsheathes his sword and declares he'll get stronger to surpass Gazef.
Hope Spot: Ainz gives this to Gazef, that he may have a chance in defeating him. Of course, it was a "HUGE" may.
Impossible Task: Ainz tells Brain and Climb that there is a way to resurrect Gazef. Unfortunately, they need a higher-tier spell to bring him back which they and the entire world don't possess.
Know When to Fold 'Em: After seeing what kind of might Ainz has, the Re-Estize nobles most definitely don't want to push their luck after he gives them an ultimatum and hand E-Rantel to him.
Nothing Is the Same Anymore: Nazarick's presence has effectively shaken the status quo of the New World. What this means is anyone's guess.
Oh, Crap!: Jircniv and his subordinates got the report from the battlefield and they are extremely horrified at just how powerful Ainz really is. It got so bad that the Emperor laughs in madness, knowing he has just done something equivalent to opening Pandora's Box.
Time Stands Still: Ainz advises to the frozen Gazef that counter spells must be deployed in case anyone uses time spells.
Underestimating Badassery: Ainz certainly thinks Gazef is duelling him because he's within a vulnerable position. He orders a Dark Young to smash the ground right beside the warrior to prove the point that the Sorcerer King is far from vulnerable.
Yank the Dog's Chain: Just when it's thought Gazef has some chance to defeat Ainz, it turns out that the latter prepared a time spell.
You Monster!: A young boy cries this out while at the same time demanding the Narzarick forces to give him back his father. He would have been killed if Momon hadn't stepped in to protect him. This is all Demiurge's ploy, who brainwashed the kid to do the deed in the first place.
