mash on something
to press on something, such as a button. (Southern.) He kept mashing on the doorbell until someone responded. Just mash on this button if you want someone to come.
mash something up
to crush something into a paste or pieces. Mash the potatoes up and put them in a bowl. Mash up the potatoes and serve them to our guests.
mash something with something
1. to use something to mash something up. Vernon mashed the potatoes with a spoon because he couldn't find the masher. Gerald used the heel of his shoe to mash the wasp.
2. to combine ingredients while mashing. Mash the turnips with the butter. She mashed the potatoes with sour cream, cream cheese, and a little garlic salt.