Unlimited Format Ruling

[DonphanAtoZ]

I have a Dialga G Lv. X active, and my opponent has Muk EX active. They have a Metagross SV and Ditto TM on their bench. Say I have four benched Pokemon. They also have Miasma Valley in play. I try to play a Magikarp on bench as a fifth basic. However, they also have Ditto TM. So would I never get to play it down, play it down and get KO'd, or just play it down?

 

[PokePop]

Sorry, this is very involved.
And, as you note, it's unlimited.
Can you note what effects you are asking about the interaction of and what you want to know works or doesn't work?

Save us the time of figuring it out since we're working on Thanksgiving preparations.