What does Baron Marinous reward?

Baron Marinous gives a choice of Mathystra Channeling Orb, Onu's Patience, 1,650 experience.

What level is Baron Marinous?

The quest log lists it at level 21.

Yes. Its quest id is not in Classic Era, so it is part of what Forever adds.

World of Warcraft: Forever · quest · level 21 · new since Classic Era

A level 21 quest in World of Warcraft: Forever in Darkshore. Recorded by 3 players running the addon.

Giver shows once a player with the addon opens the quest.

Bring the Clouded Water Globe to Onu at the Grove of the Ancients in Darkshore.1

Item	Given	Item level	Vendor sell
Mathystra Channeling Orb	as a choice	21
Onu's Patience	as a choice	21

What does Baron Marinous reward?: Baron Marinous gives a choice of Mathystra Channeling Orb, Onu's Patience, 1,650 experience.
Where does Baron Marinous start?: It was picked up in Darkshore.
What level is Baron Marinous?: The quest log lists it at level 21.
Is Baron Marinous new in WoW Forever?: Yes. Its quest id is not in Classic Era, so it is part of what Forever adds.

What sells at this level, and what to keep from these rewards, is in the level 20 to 30 gold guide.

Source: what players running the addon saw in the quest windows; the quest text itself stays in the game. Every quest seen · Darkshore