The whole ale-making town banding together to try to get the sword out of ground. Granted they can't manage but it's still a worthy effort nonetheless. Followed nicely by Meliodas pulling it out to give the town back its water flow.
Meliodas catching Gilthunder's lance and throwing it back to him...to the castle he threw it from in the first place.
Ban's escape from Baste Dungeon; up till then he's been willingly allowing them to hold him in prison, even letting them pin him to the wall with stakes and chains. When he hears Meliodas and Diane are fighting outside, he frees himself and kicks the cell door open. One of the Holy Knights tries to stop him only for Ban to dodge every slash in such a way that not only does he come out unscathed, it cuts off his beard and gives him a haircut.
Elizabeth walks into a cloud of bugs to save a child caught in it, but the child turns out to be an illusion made by one of the Holy Knights and tries to beat her to death while gloating. He stops to reveal what caused his power, the bell in his staff, only to find it gone. Elizabeth smirks and spits it out of her mouth. With the bell gone, the spell that was causing Meliodas and Diane to see each other as said Holy Knight breaks and they promptly save Elizabeth and hand the asses back to the Holy Knights who were attacking them.
Pretty much anytime King fights. He managed to find a way to subvert Ban's immortality and completely owns Geera throughout their match when even Meliodas, Diane and Ban were having trouble with her.
Meliodas likewise gets one at the end of the fight as Geera had figured out how his power works by limiting her explosions so it won't harm her when he deflects it back at him and taking advantage of the opening it brings. After King gets involved and curb stomps her, she loses composure and tries to attack him with a full force explosion. Only for Meliodas to rush in and reflect the blast back at her, beating her.
Ban vs Meliodas during the fighting festival. Both of them go all out, with both of them using techniques that would probably kill normal people.
After the Tournament two holy knights, including a stronger Geera, attack the sins, with Geera defeating Meliodas, and the other defeating Ban. Then, King, with the help of his sacred treasure, effortlessly curb stomps both of the holy knights in only a few seconds. This, more than anything, demonstrates the difference in power between a sin with his sacred instrument, and a sin without it.
When Meliodas went into his dark mode he easy defeated Geera and Jericho without a Sacred Treasure and overwhelming Helbram who has the power of 20 Holy Knights and even took Hendricksen to make Helbram borrow a little bit of his power.
Diane shows just how powerful she can be with her sacred treasure Gideon by throwing a small mountain on top of the holy knight who injured Meliodas.
Meliodas shows how strong he really is by using a twig to cut a mountain in half and use a real sword to slay a beast in many pieces.
When Elizabeth give Meliodas Liz's sword, he used it to kill the Armor Giant by slashing it into three pieces, but then cut into many tiny pieces instead.
When Elizabeth was kidnap by a unknown Holy Knight, instead of running toward Liones, Meliodas ordered Diane to toss him along with Ban and Gowther to Liones in a quick way.
After landing in Liones, a bunch of Holy Knights used several attacks on them, Meliodas just used Full Counter and defeated six Holy Knights with ease and still continued to defeat the others while rushing in.
While in prison, Hawk wanted to use the toilet so badly that he break through a iron door and defeated a knight while protecting Elizabeth.
Everything about the fight between King and Helbram. It seems King has been holding out on us...
In chapter 81, the freed Gilthunder chops off Hendricksen's hand to save Meliodas.
Not to mention that Meliodas was fighting against three Great Holy Knight class powers at the same time.
King Arthur, due to being able to embody Badass Normal by Going head to head with Hendrickson with no holy knight powers of his own. Let me repeat: He has no special magic or powers, he's just a really, incredibly skilled swordsman.
Merlin curbstomping her former apprentice, Vivian, who is said to be strongest mage in Leones.