Water

Water is a recurring substance in the Mega Man franchise. Water is harmless by itself, but can be hazardous under certain circumstances. Those include being pushed, pulled, or harmed by water, and water appearing as replacements for Bottomless Pits.

As most playable characters are machines, they can stay underwater without side effects, and they are able to jump heighter due to buyoancy. However, in Mega Man Zero 4 it is shown that ZeroXorZ can't stay on deep areas for too long, suggesting that some Reploids would not be able to stand the pressure.

In the Mega Man ZX and Mega Man Legends series human-like characters can't submerge as they can't breath underwater, only swimming on the surface in Mega Man ZX or requiring a breathing device in Mega Man Legends 2.