Mavis heads off up hill, clinging to the shadows.
OOC:
Mavis has +9 to stealth. If the giant is surprised, and she hits (with adv) then her first hit will count as a crit.
Can I suggest:
Mavis creeps down the corridor and waves for you to follow so you remain at a distance. When we find the giant, Mavis will stealthily approach and hopefully deliver the crit.
If the giant is surprised:
A crit will be 6d6+2d4+4 = average of 30 damage. It definitely won’t kill it - but it should upset it.
Then she bonus action dashes away (no opportunity attacks if it’s surprised).
By dashing away we might be able to pull the enraged giant into a trap. What trap? I don’t know. Do we have oil we can burn? Or any spells that would be useful? Are there props we can remove to drop the roof on it? Boulders we can roll on it?
It’s based on the assumption that we’ll just find a lone hill giant, and +9 stealth is enough to fix a bad roll.