Hi! So here are some pictures.
Step 1: Materials
You are going to need beige,green (or red), and white clay. If you want you can use an eyepin/headpin to make it into a charm.
Step 2: The Bottom Part
Take your beige clay and roll it into a log. Flatten the top and bottom to give it more shape. Tip: If you dont want finger prints on it, take some plastic wrap and gently place it on and squeeze around your creation.
Step 3: The Top Part
Now, take your green (or red) clay and roll it into a ball. Then flatten it. Not completely, so there is a dome like shape in the middle. Now smooth it out with your fingers.
Step 4: The Spots
Put the red piece on top of the beige piece. Now divide your white clay into to 5 small balls. Then take one and flatten it and place it on. Do that with the rest until there are two on each side of the Mushroom and one inbetween. Voila! You've made your own Mario mushroom! If you have any questions, you can ask in the comments. Thanks for reading! ~TheCraftyperson