Full summary, thanks to redon from MangaHelpers Forum.

Chapter 1,039: “Key Performer”

In the cover Color Spread, Straw Hat crew is walking through a dense forest looking for adventures.

Chapter starts in the sky over Wanokuni. Momonosuke is grabbing the “Flame Clouds” surrounding Onigashima island and is pulling them. Little by little, Momonosuke is moving Onigashima away from the “Flower Capital”.

Momonosuke: "I'm doing it...!!
I'm moving the island.
Little by little I'm moving it away from the city...!!
I won't let something like this...
falls on the capital~~~~~~!!!"

Suddenly, Momonosuke hears something.

Momonosuke: "Huh? Has someone called me?"

Cut to the Live Floor, right after Kid's attack on Big Mom from last chapter. Kaidou's subordinates can't believe they managed to attack Big Mom like that. Kid Pirates and Heart Pirates are euphoric for Kid and Law attacks. Big Mom wakes up in pain.

Big Mom: "... Ueeh!!"

Kid: "Hah, hah.
It worked, damn old hag...!!"

Law teleports to the metal bull created by Kid and talks to him.

Law: "Hey... Eustass-ya...!! That's the second time you've done it!!
After my big attack... You go and do a flashier one that seems the winning attack...!!
I'm not your fucking support artist!!"

Kid: "What's that got to do with me!!!
Stop saying stupid things!!"

Law: "If you think that, then next time you should attack first.
Then I can finish her off myself."

Kid: "Don't give me instructions!!!
It will be my special attack the one that will finish off that old hag!!"

Law: "Um... After a bull... A hippopotamus? Or an elephant?"

Kid: "Shut up!! Do you really think I'm going to reveal the trump card that I have in my sleeve!!"

As Kid and Law argue, Big Mom stands up. We see that something has happened to Big Mom's right arm.

Kaidou's subordinates: "Look at Big Mom's bones!!"

Big Mom's radius and ulna have been broken and she can't move her hand.

Big Mom: "A shockwave attack from the inside...
My ribs are wrecked too...!!!
Trafalgar's techniques are pretty dangerous...!!"

Big Mom creates a sphere with Soru Soru no Mi powers and brings it close to her broken arm.

Big Mom: "I give you life!! Revive, my bones~~~!!
Ma~~~mamama, hahaha!!!"

Big Mom heals her own arm, she is overflowing with energy, black lightning comes out of her body. Kid and Law keep talking.

Law: "This is not a joke... Hah... Hah...
After the next round, I will run out of energy...!!!
My next attack will be my last...!!
I definitely won't miss...!!
So you have to do..."

Kid: "Don't give me orders!"

Big Mom prepares to attack.

Big Mom: "Prometheus!! Napoleon!!
Hera!! Let's go!!!"

Prometheus/Napoleon/Hera: "Yes Mama!!!"

Big Mom: "“Maser Saber” (Roaring Light Sword - 鳴光剣 (メーザー サーベル))!!!"

Kid: "Uohh!!!"

Big Mom combines her 3 Homies into one sword (just like the one she used against Ulti) and cuts the metal bull created by Kid in one blow.

Kid: "...!!
It's useless!! They're just pieces of metal!!"

Big Mom: "Hah, hah.
Mamamama, you are wasting your time.
Your dream is coming to an end
little brats!!!
We have sent hundreds of young pirates like you to the bottom of the sea.
We have “ruled” this ocean for decades!!!"

As Big Mom says this, Kid jumps off his metal bull and attacks her. Big Mom tries to attack Kid too with her fused sword. But Kid is faster.

Kid: "“Assign”!!
“S”!!!
“N”!!!"

Big Mom: "Ehhh!!?"

Kid puts an “S” on Big Mom's forehead and an “N” on a half-destroyed tower from Live Floor. Then Big Mom sticks to the tower like the 2 opposite poles of a magnet. Kid returns to his metal bull and prepares to charge at Big Mom again.

Homies: "Dodge it, Mama~~~!!"

Kid: "Take this~~~~~~!!!"

Big Mom manages to flip her body with the tower stucked to her back. This way, Kid's bull hits the tower instead of Big Mom. Kid can't belive Big Mom's strength. She then uses a new attack on Kid.

Big Mom: "“Bahouhou” (Visiting Mother Cannon - 母訪砲 (バホウほう))!!!
“Misery” (3000 Leagues - 三千里 (ミザリ))!!!"

Translator's note: Big Mom's attack is based on the Anime “3000 Leagues in Search of Mother” (Haha o Tazunete Sanzenri).

In an amazing double page, Big Mom uses her fused saber to create a giant woman of fire and thunder that attacks Kid. As Big Mom laughs and wonders if Kid is alive, a piece of a tower appears above Big Mom's head.

Big Mom: "Eh?"

Law: "Takt."

The tower crushes Big Mom as Kaidou's subordinates run away from the rubble. Law jumps at Big Mom, he coats his sword with a “K Room”. Kid is still standing, but he has many injuries.

When she's getting up, Law stabs Big Mom's chest.

Big Mom: "Damn you~~~~~~!!!
Trafalgar~~~~~~~~~~~~!!!"

Cut to the basement armory, we see Law's sword has also passed through this floor of the castle.

Yamato: "What is that!!!"

Cut to Wanokuni, we see Law's sword stabs the land of Wanokuni below Onigashima island.

Back to the Live Floor. Big Mom coated her fists with Haki and is hitting Law until he's near dead. But Law doesn't let go of the sword becouse he's making it go deeper and deeper.

Big Mom: "Release me now!!
Trafalgar!!!"

Law: "...!!"

Heart Pirates: "Captain!!"

Law: "Must go...!!
Deeper!!"

Big Mom: "What happened!?
Weren't you already out of strength!?"

Heart Pirates: "What are you doing!? Captain.
Get away!! She's going to kill you!!"

Law finally completes his attack.

Big Mom: "Huh!?
Stop..."

Law: "“Puncture Ville” (Puncture Shockwave - 穿刺波動 (パンクチャー ヴィレ))!!!!"

Big Mom: "Uehhhh~~~~~~!!!

The shockwave from Law's attack goes through the entire Onigashima castle and produces a powerful explosion in Wanokuni. The explosion creates massive hole in the ground of Wanokuni below Onigashima island.

Big Mom screams in pain and spits blood out of her mouth again. Momonosuke looks from the sky the big hole that has been created in Wanokuni. Yamato looks at the roof of the armory and wonders what created that hole.

Despite Law's attack, Big Mom is still standing and attacks Law with the giant woman of fire and thunder

Big Mom: "Burn him until he dies, “Misery”!!"

Misery: "Yes, Mama!!!"

Law: "Hah.
Hah.
Do it now!!
Hah, hah.
Eustass-ya!!!"

Big Mom: "What!? What the hell is that!!!"

Kid: "How many times do I have to repeat it!!
Trafalgar...!!
Don't give me order!!!"

In another fantastic double page, we can finally see Kid's trump card. He has created a huge electromagnetic cannon with which he's aiming at Big Mom from the air. Kid prepares the cannon while Law laughs confidently.

Big Mom: "Damn!!!"

Big Mom turns to Kid defiantly, ready to face his attack.

Big Mom: "Come on!!! Go ahead!!!
Do you think you can defeat me!!?
I am “Big Mom”!!!!"

Kid: "I'm going to finish you off...!!!
“Damned Punk” (Magnetic Cannon - 電磁砲 (ダムド パンク))!!!!"

Big Mom: "Oooooooh!!!"

In an epic final double page, Kid fires a powerful beam that hits Big Mom's body, who falls to the ground spitting blood from her mouth. In the last panel of the chapter we see Law.

Law: "Your era ends here!!!"

End of the chapter.