The newly advanced Charisian Navy proceeding to utterly curb stomp the combined naval might of the entire world.
Don't forget forget when Merlin kills a kraken (think twenty foot long shark with tentacles) that was attacking a boat with a harpoon from seventy yards away, then proceeds to jump in the water and gut the remaining two with his sword.
In the same scene, one of the boys being attacked risked his life to save the younger children.
Merlin rescuing Earl Grey Harbour from the traitor Duke Tirian by crashing through a skylight in the midst of Dramatic Thunder, and proceeding to massacre 15 guards in something less then a minute, and then Grey Harbour kills the duke with a thrown dagger, despite the dagger not being balanced for throwing, the Earl being middle-aged and out of practice, and also being fairly drunk at the time
By Schism Rent Asunder
Maikel Staynair's going up and giving a sermon about forgiveness moments after a failed attempt on his life occurred right there in the church.
We can't leave out Dynnys Erayk, who undergoes a Heel-Face Turn while getting reacquainted with the true meaning of his faith while in prison for treason as the church's scapegoat. He faces horrific torture unless he publicly repents his actions in exchange for a quick death, and agrees... then uses his time in public to declare that the accusations against Charis were all lies and the fault lay in the church being corrupt enough to use them for an excuse to invade.
The Brotherhood of Saint Zherneau's reveal qualifies. Father Zhon begins to recite the "truth" that the Charisan kings have been ruling by.
The last stand of Sharleyan's Imperial Guard, complete with Sharleyan herself providing cover fire. This act served to delay the attempted assassins long enough for Merlin to arrive on the scene and save the Empress and the Guard's sole survivor.
A Mighty Fortress
Madame Ahnzhelyk Phonda successfully smuggled over 200 potential victims of the Inquisition to safety, some right out of the temple city of Zion, by a combination of Crazy Preparedness and a level of Refuge in Audacity that left Cayleb "almost reverent." The first stage of this plan: Smuggle people aboard iceboats carrying shipping with Grand Inquisitor Clyntahn's name on it, right on the heels of Clyntahn's purge of his opponents which necessitated their escaping the city in the first place. Thus ensuring that nobody would dare disturb it.
Hauwerd Wylsynn's last stand against the Inquisitors and Temple Guards Clyntahn sent to arrest him, during which he fights and kills five armed and armored men before dying himself, dropping a couple of Precision F Strikes for good measure.
The Markovian Sea battle. The first battle on the planet to feature the use of signal rockets and exploding shells. Decimating the Navy of God just as the Church was finally getting back on its feet following the disasters in Off Armageddon Reef. The Navy of God boasted nearly 140 ships, outnumbering the hastily thrown together Charisian force sent to intercept it about four-to-one. As noted in How Firm A Foundation less than ten make it back to safe harbor without being sunk or captured.
It's never stated, but when you stop and think about it, everyone in the Inner Circle other than Merlin has gone from a (albeit rapidly declining) Medieval Stasis to a level of basic skill with some of the Old Terra technology Merlin has available in the course of roughly two years, such Owl and the coms. Cayleb's comfortable enough with it to use Owl to keep track of baseball scores. This is after Merlin had to explain to Cayleb that one reason he couldn't explain his nature was because Cayleb lacked the very foundation necessary to even imagine things like a PICA, and Cayleb confessed that until seeing the recon skimmer he'd still half-thought of all the lost technology as magical.
How Firm a Foundation
Captain Dunkyn Yairley and the crew of the HMS Destiny in the opening chapters, as they pull off some epic MacGyvering to save the ship from being wrecked against seemingly impossible odds.
Sharleyan survives an assassination attempt while meting out judgement (and mercy) to the members of the Northern Conspiracy. Though what's truly awesome is the fact that, despite protective clothing provided by Merlin, the bullet that hit her still broke some of her ribs and, despite that, Sharleyan finished out the whole day's work, showing no sign of her injury until she was away from everyone.
A Dying Moment of Awesome for Prince Nahrmahn, whose heroic sacrifice in throwing himself over his wife is the only reason she was the sole survivor on the attack on their carriage.
Gwylym Manthyr was captured by the enemy, turned over to the Inquisition, suffered months of travel in highly unhygienic conditions, was brutally tortured, and then taken to be publicly executed. When asked if he had any last statement to make by the Grand Inquisitor (Who knew full well that the man's tongue had been cut out), he spits in his face.
Sixteen year old lieutenant Hektor Aplyn-Ahrmahk, in the climax of the book, taking command and completing a rescue mission when about two-thirds of the company, including senior officers, were too injured to go on. He also fulfills Cayleb and Sharleyan's proclamation that Inquisitors would be shown no quarter. Also bear in mind that, due to the difference in Safeholdian and Old Terran years, Aplyn-Ahrmahk is closer to fourteen years old. He delivers an epic "The Reason You Suck" Speech to the Inquisitor in question before calmly shooting him in the head.
Sailys Trahskhat may be a Temple Loyalist who thinks of his fellow Charisians as heretics, but his defending his family from a murderous anti-Charisian mob with his lucky baseball bat is pure awesome.
Merlin introducing the revolver to Safehold by gunning down nearly a dozen men, including two of Clyntahn's direct subordinates.
Not as action-oriented, Paityr Wylsynn, now let in on the secret history of Safehold, gleefully demonstrating why having someone who's normal job is to prevent Loophole Abuse is a great friend to have when he's actively helping you exploit them.
Also, there is Merlin's borrowed Moment, where there are some good men behind him, and a (reluctant) villain in front of him. The discussion does not end well.
Midst Toil And Tribulation
HMS Delthak and her sister ships are iron-clad moments of awesome. Especially their raid up the canals.
Earl Hanth's ambush of the Dohlaran army at Thesmar, disguising some of his sailors as farmers as a lure while the majority of his men hide in the woods that the cavalry scouts wouldn't think to check.
Like a Mighty Army
"Dialydd Mab" and his Roaring Rampage of Revenge against those responsible for atrocities at Sarkyn. Atrocities which cost the lives of seventy percent of its population. What we see on-page is his attack on the barge with the Inquisitors who actually ordered everything and their Army of God escorts. What we learn later is that he also went to the Sarkyn garrison and killed its commanding officer, his second-in-command, his third-in-command, all commanders of the infantry companies assigned to cleanse Sarkyn and escorting prisoners to concentration camps, and any and all lower soldiers who "distinguished" themselves Sarkyn's cleansing. To top it all off, he leaves a letter containing a scathing "The Reason You Suck" Speech addressed to "Zhaspahr Clyntahn, Grand Fornicator."
More awesome from the HMS Delthak, when it launches an insanely dangerous rescue mission to save one of the ships it's sailing with after the galleon's masts are torn off in a fierce storm. They successfully rescue and tow a ship that otherwise would've been completely doomed.
While already very impressive, Aivah Parshahn proves her awesomeness in the final words of the book's epilogue, when she's reminded why a favor she's asking of Merlin, to be able to make a trip in and out of Zion within a day on short notice, should be impossible.
Aivah: That's why I'm speaking to you about it... Ahbraim.
Archbishop Klairmant Gairlyng's prayer upon Irys and Daivin's return to Corisande, first giving Irys as much official power as her brother, then declaring openly that Corisande will be joining the war against the Temple Lands.
Nimue teaching a lesson to a Jerkass guard who's still on Clyntahn's side, first giving him every chance to get out with his dignity intact so the numerous spectators all agree she was right. Merlin and Cayleb take a great a great deal of pleasure watching a recording of the fight while munching fries and drinking beer.