Dude, it's mashed potatoes. Stick it in the microwave for a few minutes and nuke whatever bacteria is in there then enjoy.

People are so germaphobic these days. What evil disease could you possibly get from food that stayed in the microwave over night?

I leave pizza in the oven for 1-2 days and heat up a piece every now and then. I do that because pizza from the fridge is nasty and the crust turns to stone. Never had a problem.