OW Ability: Fortify

Helpful against Mei as it prevents freezing, whether it be her primary fire or her ult.
It can also help you survive against Reaper: with reduced damage, not only will it keep you alive longer, but it also reduces how much he can heal. While the Fusion Driver can easily deal more damage than he could heal while fortified, if he catches you by surprise or during your cool down, that will not save you. Even if you do survive, without some healing, you will be low on health.