SMG4: The Minecraft Plague is the thirty-third episode of Season 9 and the five hundred and twenty-fourth overall to be uploaded by SMG4.
This episode was aired on September 7, 2019.
Meggy and Boopkins stumble upon a mysterious Minecraft block...
The episode opens up with Meggy Spletzer going for a swim, taking advantage of her humanity. However, Fishy Boopkins chooses to be a showoff. Just then, a Minecraft grass block floated over to Boopkins. Shocked into thinking someone else was with them, he pushed the block onto some sand.
Just as they turned around, they saw the block. Wondering what was it doing near them, they touched it. The block then activated, resulting in the area slowly becoming Minecrafted. Boopkins was next to the block so he became Minecrafted first. As Meggy looked on shocked, a parrot flew and landed on him, getting it Minecrafted too. Knowing she couldn't let this happen, Meggy rushed off to get help.
In Peach's Castle, Mario was practicing his knife throwing skill at Toad (who was tied up and threatened to hurt him once he was freed) by aiming at an apple on his head in front of Tari and Luigi because apparently, Mario saw the act on TV. Just then, Meggy burst through the door, freaking Mario into flinging the knife. It landed right onto Toadsworth's head, killing him. As Meggy explained the situation, it suddenly showed up. Mario, Luigi, Tari, and Meggy freaked out upon seeing the castle get Minecrafted fast. Toad who was ignorant at first started screaming in pain while being Minecrafted. Tari tried to stop it by touching Toad but she got her hand stuck by it and now also gotten Minecrafted (even changing her speech font).
As Mario was freaking out by the transformation (once again mistaking Minecraft for Roblox), the rest saw how the Minecrafting took over the castle. Just then, Meggy had an idea. Having Mario turn into a spear, she threw him through the unaffected wall easily, allowing them to escape. Seeing with horror what the Minecrafting did to the castle, Mario said they needed help of someone.
That person turned out to be Steve. As he was heading inside a disused washing facility to wash his equipment, Mario, Luigi, and Meggy appeared. As they explained what was happening, Steve saw for himself how the Minecrafting was happening. He thought about it and upon seeing that he had one hour left until the washing was done, he agreed and told them to follow him.
At his house in his basement, he showed them a plan for a gun. Although Meggy showed her doubts, Steve assured it would work while Luigi was optimistic due to only needing to get the materials. Suddenly, the Minecrafting caught up with them. Steve quickly saved them by lifting all of them up and then threw them and the gun recipe into the world of Minecraft.
As they wondered how to get the materials, Luigi started by breaking blocks from a tree like a sensible player but Mario wanted to go faster by taking the block Luigi dugout and throwing it at a villager, killing it and getting its equipment.
In a mine, Mario tried to use the diamond pickaxe to dig out gems but it broke, causing him instead to make the mine a hotel for Creepers and then spooking them into exploding with a spider. It worked fine. Meggy though was attacking a Skeleton archer for its loot. They had a short duel before Meggy triumphed and took its loot.
As Luigi managed to break three blocks of wood and having broken hands, he noticed that Mario and Meggy achieved a lot more than he did. To cheer him up, they agreed that Luigi did help out.
Later on, Mario put all the items needed to make the gun on a crafting table. It failed, however. Upon reading the recipe again, they noticed that they needed a human soul. Luigi offered to sacrifice himself but Mario took a villager and used its soul instead, causing the gun to be created. Testing the gun's Anti-Minecraft setting, it turned a tree and a villager into a realistic tree and Squidward Tentacles respectively.
Now wondering how would they get out, Meggy screamed out for Steve about returning everything back to normal. Steve noticed how he still had an hour left before his washing was finished, causing him to use a fishing rod to drag them back into the Mushroom Kingdom (while ensuring they were on a table to prevent them from being Minecrafted). Mario then used the gun to turn Steve's house back to normal. Mario then declared that he would be getting rid of everything relating to Minecraft back to normal except for Steve. Agreeable, Steve became Captain Steve and flew Mario across the Mushroom Kingdom, turning everything back to normal.
Now that everything was back to normal, Mario, Luigi, and Meggy went off to celebrate, hoping that Mario did not miss a site. However, it turns out that somehow while reverting the castle back to normal, Mario has forgotten about Boopkins and the parrot. A creeper then went up to him and became attracted to him, much to Boopkins' dismay.