The PureStreamV person in chat is referencing KyoStinV Very well known in the Arknights community for making video guides on how to get through stages and events, especially time limited ones like Contingency Contracts. He also makes guides on getting through stages with low(er) tier operators. Melantha is very often used, so "Activate Melata Skill" is something you will hear quite often.
Probably a Blackshield (A Deathwatch marine who has cut ties with his chapter). There are chapters which use black for the right pauldron, but you should be able to see at least a bit of his chapter's emblem from this angle with how big they are.
