As Mario, being juggled by Snake is very likely to happen. Snake up-air is really good and could send you far upwards and is a great juggling tool. When being juggled, Snake doesn't always have to up-air. Snakes Nikita is a great tool, and hits opponents upwards. The best option is usually to fast-fall nair, but it could be good to fast-fall into the ground then air-dodge downwards. You could follow the downwards air-dodge with a tech-roll away, or tech-roll in. Just be careful, as neutral tech isn't always safe, nor are the rolls. So mix it up with DI, fake-outs, fast-falls, and nairs to get back into neutral.
Mario