Leave the cream cheese on the counter until it feels soft when pressed. Cold cream cheese leaves lumps that never fully blend out. I usually set it out about 30 minutes before I start.
Add the softened cream cheese to a large bowl. Beat it on medium speed for one to two minutes until it looks silky. If it came straight from the fridge, it may need a little longer.
Spoon in the marshmallow fluff, then add the salt and green food coloring. Beat again on medium speed until everything looks even and smooth. Taste it and add a drop or two more color if you want a bolder green.
If you are using M&M's, stir them in by hand with a spatula. Do not use the mixer here, or the candy coating will bleed and turn your dip a muddy brown. Gentle folding keeps the colors bright.
Move the dip to a serving bowl and cover it. Refrigerate for at least 20 minutes so it firms up. A longer chill is fine if you are prepping ahead.
Wait until just before serving to press the eyeballs into the top. If you add them too early, they can slip or get soggy. Mix big and small eyes so the dip looks like a funny monster family.
Set out the bowl with a pile of dippers around it. Strawberries, pretzels, and graham crackers are always the first to go. Let the dip sit out about 15 minutes if it feels too firm to scoop