The heroes have their reputation not for nothing. Even though Laslow joined them relatively late, each of them had their great heroic moments, which I am about to list here. I reduced the list to three this time tho, I hope you don't mind. 

Let's start with Mari: 

#3 The Varya Heroine

After Mari obtained the Gardevoirite, Saizo tried forcing her to give it up and hand it over to him. She wasn't having any of that and instead activated Mega Evolution to kick his ass in battle and make him surrender. In the end, Saizo descended from his hill of pride and apologized to Mari in front of everyone, making every single ninja bow to her out of utter respect. 

#2 Kyurem's Downfall

When Kyurem regained its final form, all hope was lost for anyone to win this battle. But then Mari had the brilliant idea of targetting Kyurem's neck, where the DNA Splicers were situated, to destroy them and get Kyurem out of its misery. She flew above the raging dragon who wanted every single person that attacked it to pay for daring to oppose it, and told Gardevoir to aim her Focus Blast at Kyurem's neck, which resulted in Kyurem losing its final form and Reshiram and Zekrom emerging from its body, taking the ice dragon down themselves. 

#1 Moon's Reckoning

When the ultimate battle against Necrozma started, Mari summoned Lunala, climbed onto its back and started fighting Ultra Beasts while engaging Lunala to open Ultra Wormholes to rip apart the giant Sky Pulse above Alola (which solely was her idea). Riding the moon's dark wings, she embarked on the path of war against Necrozma, never once relenting. 

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Jacky

#3 Nightmare Breaker

When Hypno tricked Jacky into choosing between her starter Pokémon, Absol, and her best friend Mari, Mari captured Hypno, holding him in place, and Jacky took the opportunity to ram a dagger into his body and break his spell at last, finally being able to end his childnapping and free all of the abducted children from Celestial Tower. 

#2 Sun's Payback

As the final battle started, Jacky summoned Solgaleo, riding into war on its back alongside Mari. She tore down ultra beasts and let her partner open wormholes to tear the big one apart, facing down Necrozma in the very end. 

#1 Monastery Raid

After Jayden revealed he obtained the Rebel Mark, Jacky told him to leave with Mari and she would take over all the fighting, leaving her back to fight more than just a few pissed nuns and monks and shove their heads pretty far up their butts.  

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Jayden

#3 Rebellion

When Jayden pretended to vow in front of Nate to serve the monastery and Arceus forever, he changed the oath and showed everyone his Rebel Mark, leaving everyone in the room stunned for a second. Not only did he do that to save Mari, but to tear down the monastery's credibility and reputation for the lies they had woven. 

#2 The Crystal of Light

When the heroes were warped to Ultra Megalopolis where they met Kalani at the tower, Jayden stole Kalani's Z Crystal which kept Necrozma under his command and so released the ruler of the Ultraspace from its torment after it had regained its light in the battle prior. 

#1 The Devil's Battle

When they faced his alter ego in the Omega World, they found themselves having to oppose the devil itself, Giratina. Jayden then took it upon himself to bring Giratina to change sides and team up with the TRUE rebel, fighting their adversaries together. Even if Jayden never was proud of his status as a rebel and traitor of the divine order, he made use of it to end all suffering in a foreign world. 

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Laslow

#3 Zeke's Shield

When Zeke and Laslow got ambushed together at the Hokulani Observatory, Laslow shielded Zeke from an attack, acquiring a very nasty injury. Even when cowering on the ground with blood staining his clothes and the ground, he continued standing his ground and fight off the beasts to protect Zeke and hold until backup arrived and he eventually passed out. 

#2 Death Battle

In the Omega World, Cecil threatened to kill Taji if Laslow wouldn't face him in a one on one final death battle. Laslow gave in eventually, fighting Cecil and his endless legion of Ultra Beasts off til the bitter end to protect Taji and end all of the suffering. Even tho Cecil perished at the very end despite his opponent trying to bring him to stop fighting, Laslow remained by his enemy's side when he drew his last breath and paid him his last respect by providing him a proper burial. 

#1 Saito's Legacy

When the woman called Mito stole the artifacts to reunite the Seal Coin, summon Ho-Oh and try to obtain its blood to gain eternal life, Laslow entered the contract of the Rainbow Bringer to free it from outside control. His hair turned golden and he ascended Ho-Oh's back as it regained its senses, taking the enemy down. His invulnerability in this stage made him get away unscathed after being hit by multiple Hyper Beams that otherwise would've turned him into a pile of dust, giving him the appearance of something similar to a literal god. 

Which one is your favorite hero and which moments of their heroism do you recall most? Let me know in the comments.