[Life Series] Up until Limited Life, nobody in the Life Series really knew Grian was a Watcher (aside from the people from Evo, obv), because it was only revealed (by accident) when Grian went AFK for one of the sessions. This is because as canonically established in Evo, the viewers are the Watchers, and because Grian was AFK, he was watching everything happen with us. Therefore, he was revealed to be a Watcher.

[Hermitcraft] Mumbo being a vampire means he can't be out in direct sunlight without getting severely burned, so he often carries around a parasol to protect himself. Sometimes Grian will ride around on Mumbo's shoulders with his wings spread to shield Mumbo from the sun. Mumbo also often hides under trees to avoid the sunlight

[Life Series] All the Winners (excluding Cleo) are made aware of the Watchers in the seasons after they've won, meaning they can hear the Watchers. Grian is mostly unaffected since he is a Watcher but is easily emotionally swayed by their whispers, Scott chooses to acknowledge but dismiss them, Pearl is easily manipulated by them, Martyn tries to ignore them the best he can, and Scar tries to be friendly with them instead of trying to fight them in hopes that they'll let up (they won't).

[Life Series] (Kind of adding onto the last one) After every season, Grian gets more and more unhinged due to hearing the Watchers and losing his sanity to their taunting whispers. He's more easily angered and starts to lose his will to follow the rules implied by the game (such as Greens can't kill unless in self-defense). Every life he loses chips away at whatever sanity he has left, leaving him to go completely mad.