Heavens!
If gengar explodes, kangaskhan grabs the chair and uses it as a substitute to shield them from the blast.
If gengar doesn't explode, and kangaskhan is underground and in danger of the waves, kangaskhan's baby barricades the hole with rock tomb to block out the waves. If rock tomb isn't enough, she uses rock slide instead.
If kangaskhan has a whirlpool that can absorb the waves, kangaskhan plays pat-a-cake with her joey in the whirlpool. If the waves can get kangaskhan through the whirlpool, or kangaskhan doesn't have a whirlpool, kangaskhan instead grabs her baby, and uses aerial ace to swoop behind lucario where it's safe, then kick it in its boxer-wearing rumpus. If that won't work, kangaskhan is probably a goner already, so meh.