Actually, what might be fun is to flip that on its head and make it a cost a player can pay to exile it when it dies, ala quenchable fire

Also, for the Boo, I was thinking, what if we have a 'turns matter' theme for them? So if it's your turn, they turn on, but otherwise they turn off?
Something like "Boo cannot block" and "If it's your turn, Boo gets hexproof"

Of course, the fun thing is there can be variety in the design file, because otherwise we'd have a rough time filling everything out...

A
Lastly, what do we think of Battalion for the Koopa Mechanic?

I like this idea. Put the onus on them to stop your Dry Bones from coming back.


Phasing. Everybody loves phasing, right?


I think it makes sense. Even in Super Mario Brothers, they would often come in groups of threes.

Here's a random idea, apropos of nothing:

Lakitu Summoner -
Creature - Turtle Wizard
Flying
At the beginning of each upkeep, if ~ is tapped, create a 1/1 red Spinie creature token with haste and bushido 1.
0/1

Maybe take a note from Inistrad's werewolves. THey can't attack/block/whichever if an opponent did something last turn. I think creature etb or being attacked are the best options. THe former seems less likely to result in lopsided matches.

You can take a hybrid approach- Mario and co have special powers that are activated through the ritualistic use of mushrooms, flowers and leaves.
Mario is a shaman.


Although perhaps we woould want to count down bricks in some cases. Or just make a creature that can bust them.


Maybe take a note from Inistrad's werewolves. THey can't attack/block/whichever if an opponent did something last turn. I think creature etb or being attacked are the best options. THe former seems less likely to result in lopsided matches.

Ice World -
World Enchantment
Whenever a creature attacks, it's controller loses control of that creature. Whenever a player loses control of a creature in this way, any opponent may pay any amount of mana. If at least one player does, the player who paid the most gains control of that creature. If no player paid the most, that creature's owner gains control of it.

Giant World -
World Enchantment
When ~ enters the battlefield, each player gains 10 life.
Creatures get +2/+2.

Desert World -
World Enchantment
Creatures with heat counters on them don't untap during your untap step.
During your upkeep phase, remove a heat counter from each creature you control with a heat counter on it.
Whenever a creature becomes tapped, put a heat counter on it.

My YMTC mind wants to streamline Desert world as "Whenever a creature becomes tapped, its controller exerts it."

Oh, yeah, that's a thing, isn't it?

Very well. Make it so.

Pirahna Plant Pipe
Artifact

If Pirahna Plant Pipe is untapped, during your end step create a 1/1 green plant token.
Sacrifice all tokens created this way during your next upkeep.


The color pie bend is REALLY big here. Desert World and Ice World really feel like they should mechanically swap because of color pie.
Though I think Water World would be more Apropos for Blue. I'll look in my Mariocyclopedia to see if there are actual level names we could use.


Dry Bones
Creature - Skeleton Turtle
Haste
When Dry Bones dies, any player may pay . If they do, exile it instead.
If Dry Bones is in your graveyard during your upkeep, return it to the battlefield.
1/1

Boooooo.



....Bushido?
Shouldn't it have Deathtouch?

Okay, so, design file time


Generic Mechanic:
Brick Counters

Mushroom Kingdom:
Totem Auras
Enchantments Matters

Yoshi's Island:
?????

Koopa Kingdom:
Battalion

Boo Kingdom:
????? (probably a turns matter theme)

Flavor resources: Creatures

Yeah, I'm just throwing ideas at the wall to see what sticks. I'm not spending a lot of time thinking about proper colors or anything. If an idea works, go ahead and run with it. If not, that's fine.

You could come up with quite a few multiverse-fitting plot ideas based on a pun in thread's title, tho.
Speaking of it...
viewtopic.php?f=17&t=18182&start=120#p634013

Do you think Bob-Ombs would be flavored as artifact creatures? And would they have "Sacrifice: Effect" abilities, or would their self-destruction be triggered based on taking damage, or maybe even just attacking?

Also, there's a disturbing lack of Monty Mole on your list.