While Marvin makes marvelous mechanical manatees Mandy makes muffins for marching marshions?

yea but maybe do Marvin makes marvelous mechanical manatees. For Mandy to fees her miraculous marching marshions for its trickier to start with a M and dive right in!! hope I helped xD

iT is okay not a tongue for me because I am really god at reading them

She sits upon the slitted sheets - upon the slitted sheets she sits.

Here's the corrected version: "While Marvin makes marvelous mechanical manatees, Mandy makes muffins for marching Martians". Note the addition of the comma, and the correct spelling of "Martians".

It's pretty good, but please learn how to use punctuation when you write. Not just in the tongue-twister, but in your other writing as well. You used almost NONE in your question, and it makes you appear uneducated even though you're not.