For the snowman rig, place a small boilie on the top and add a standard-sized boilie on the bottom. The snowman stands up on the bottom, making it look like a snowman. This rig is often used by anglers to target large carp, but it will hook a variety of fish. The best time to give it a try is when you are having a hard time getting bites using other lures and rigs.
Another option is the reverse snowman, where the big boilie goes on the top and the smaller one is on the bottom. The reverse snowan looks like an upside-down snowman when it sits on the bottom. If you have boilie extenders, you can use them to make the reverse snowman rig look better.
You can try many different variations of boilie set-ups for this rig until you find the one that presents itself best for the type of fish you are targeting.