After awakening the powers of the Gomu Gomu no Mi, also known as the Hito Hito no Mi, Model: Nika, Luffy was able to tap into the power of the incredible Gear 5th form in the fight against Kaido on the rooftop of Onigashima.
Gear 5th sees Luffy reach his very peak as a fighter and gain even further strength, reaching levels closer to Yonko Kaido and becoming worthy enough to match him in combat. Although Luffy has not used Gear 5th for long, he has already demonstrated quite a few techniques to the fans in his attempt to crush Kaido atop the roof of Onigashima in One Piece's Wano Country arc.
6 Gomu Gomu no Fusen
Gomu Gomu no Fusen, also known as Gum Gum Balloon, is a standard Gomu Gomu no Mi technique that Luffy can utilize without entering any Gear. In Gear 5th, Luffy can make use of a stronger version of this technique. Since his rubber body is much tougher than before and has more freedom, this technique can bounce off blunt attacks with ease, regardless of how powerful they are. At the same time, Luffy can also use it to hurt others.
When Kaido swallowed him, Luffy used this technique inside his stomach and, due to his awakening powers, turned him into a rubber balloon too. Upon being stretched like a balloon, Kaido felt immense pain and couldn't help but scream. Luffy could very well have continued to hurt him for longer but chose to use other techniques shortly after.
5 Gomu Gomu no Dasshutsu Rocket
Dasshutsu Rocket, or Escape Rocket, is a technique that Luffy can utilize only in Gear 5th, unlike Gomu no Fusen. This technique is more of a situational one as it doesn't see him attack his enemies in a standard way. In a way, it can be seen as a stronger version of the Gomu Gomu no Rocket. Luffy used it after being swallowed by Kaido. Following expanding his body within him to hurt him, Luffy looked for an opening and stretched his arms through Kaido's eyes to grab his snout.
Then, Luffy used the immense force generated from the stretching of rubber to eject himself from Kaido's mouth. Although this technique can only be used to escape from within something, it is still quite a useful ability. Sadly, it doesn't deal much damage apart from stretching the eyes of the opponent. Nonetheless, Gomu Gomu no Dasshutsu Rocket is quite an interesting ability.
4 Gomu Gomu no Nawatobi
Also known as Gum-Gum Skipping Rope, this is another one of the situational techniques that Monkey D Luffy used in his fight against Kaido on the rooftop of Onigashima. This technique sees Luffy grab Kaido's head and tail and spin him like a skipping rope. Although this technique did humiliate the Yonko quite a bit, it doesn't have much usability other than that.
At best, this technique would make the target quite dizzy and ruin their balance, however, it is also quite easy to counter. In the fight against Luffy, fans saw Kaido counter this technique with his Borobreath and char Luffy completely. This is quite easily one of the weakest techniques that Luffy has deployed while using his Gear 5th.
3 Gomu Gomu no Kaminari
Gomu Gomu no Kaminari, also known as Gum-Gum Lightning Bolt is quite a powerful technique. Once again, Luffy used this technique after awakening his devil fruit in the fight against Yonko Kaido in One Piece's Wano Country arc of One Piece. Using the powers of his awakened devil fruit, Luffy grabbed a lightning bolt from the sky and turned it into rubber.
The lightning bolt was then hurled at Kaido at a tremendous speed and would have electrocuted and burned him had it hit. Thankfully for the Yonko, the incredible physical prowess offered by his Mythical Zoan dragon Devil Fruit allowed him to dodge the attack and launch a successful counterattack on Luffy. While the attack didn't work, it is quite easily one of the strongest that Luffy has ever used in the story so far.
2 Gomu Gomu no Gigant
Also known as Gum-Gum Giant, Gomu Gomu no Gigant is quite a powerful technique that takes Gear Third to a whole new level. Just like how Luffy increases the size of his limbs while using Gear Third, this technique sees him use it on his entire body and turn into an actual giant. Being used in Gear 5th, Gomu Gomu no Gigant is much stronger than Luffy's Gear Third techniques.
This technique saw him increase massively in size comparable to that of an island itself and even someone as massive as Kaido in his dragon form looked quite small compared to him. Luffy was seen trying to stomp on Kaido when using this technique, however, the Yonko successfully countered by biting him. Luffy then proceeded to use the skipping rope technique to free himself from the Yonko's grasp. When used in combat, this is quite easily one of the most dangerous techniques as it increases his size, and thus his attacking power, to sky-high levels.
1 Gomu Gomu no Bajrang Gun
Gomu Gomu no Bajrang Gun is Luffy's strongest technique in the series so far. Its application is quite similar to Gear Third, however, it is much bigger in size. Bajrang gun sees Luffy create a massive fist the size of an island. Luffy then proceeds to coat this fist in advanced forms of Armament and Conqueror's Haki.
This technique was powerful enough to match Kaido's Flaming Drum Dragon technique, and overpower his Haki as well. Bajrang Gun was able to break through Kaido's defenses in his strongest form. The power of the technique was such that Kaido was sent crashing down at blinding speeds. The ground Kaido crashed into left a dragon-shaped hole and the Yonko got buried underground, completely being knocked out by its sheer strength.