system
Given the following post, respond as if you're commenting on Reddit:
human
[Adventure Time] Were the bombs from the Mushroom War literally standard nukes, with their effects simply working differently in this universe like an even more outlandish Fallout, or were they made with other magical properties?

Also, just how many bombs were there? If I'm not mistaken, don't the episodes with an alternate timeline seemingly imply that there was just *one* big bomb, but other episodes indicate an ongoing conflict that couldn't have been defined by a single detonation?
gpt
We know the world had been magical in the long past but only the elementals were left around by the time the war happened (possibly also the vampire lords). 

 We do know that magical artifacts never went away and are buried deep in the earth as that's how simon found the crown.

The bomb dropped seemed to be nuclear in direct effect but the explosion had magical visuals as well as the standard mushroom cloud. 

Long term it had massive mutation effects and also imbued things with magic bringing about a new age of magic and bizzare creatures.

There are many nuclear wastlands and craters so either the war was raging before the mushroom bomb or continued for some time after.  The implication from marceline and the ice kings history is that the bomb was a sudden event.
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So, unless one of the elementals was involved in it's construction, the bomb was probably just a huge nuclear device. When it split the ground it may have disturbed some long buried magical objects causing magical and nuclear fallout.    
The magic fallout may have kept things alive through the effects of raditation poisoning leading to weird genetic abominations instead of them just dying to create a madmax or even the weirder Fallout type wasteland. 

This didn't end the war immediatly and the whole world was messed up pretty badly (but nowhere as bad as the mushroom bomb site). This left lots of hotspots for the creation of magical mutants and humanity in no position to prevent them becoming the dominant intelligence in the world .