I don't know your plans for the Sea Hag, so I'll take a different tack on my response.
I'd say this is fair even if it results in a TPK because players sometimes need a refresher course in "Sometimes you win the fight by not fighting 101"- aka tactical thinking. And this, of course, also includes the tactic of running away when overmatched.
A Sea Hag could make a nice recurring villain/NPC for a low level party...especially if you're the type of DM that allows even monsters/NPCs to "gain XP" and plays opponents up to their statted level of intelligence or craftiness.
When the party finally gains enough XP to finally take her down, it might be the most memorable moment in the campaign up to that point. A significant milestone in the development of the PCs.
So, yes- use the Sea Hag.
Worried about player expectations? Don't be. A good melee that results in a TPK can be as fun and memorable as a decisive victory.
I don't know your players at all, but I remember my first adventure 28 years ago. My Fighter and another player's Wizard were the only PCs that survived until the pentultimate room, where we both fell in battle to a purple worm. That final battle was epic, and turned on a few key rolls. Neither side pulled punches or fudged rolls either- everything was in the open.
And despite the TPK, that adventure had me hooked for life on this hobby. If I hadn't moved away that summer, I'd have played at that DM's table again in a heartbeat.
So, yes- use the Sea Hag.
I'd say this is fair even if it results in a TPK because players sometimes need a refresher course in "Sometimes you win the fight by not fighting 101"- aka tactical thinking. And this, of course, also includes the tactic of running away when overmatched.
A Sea Hag could make a nice recurring villain/NPC for a low level party...especially if you're the type of DM that allows even monsters/NPCs to "gain XP" and plays opponents up to their statted level of intelligence or craftiness.
When the party finally gains enough XP to finally take her down, it might be the most memorable moment in the campaign up to that point. A significant milestone in the development of the PCs.
So, yes- use the Sea Hag.
Worried about player expectations? Don't be. A good melee that results in a TPK can be as fun and memorable as a decisive victory.
I don't know your players at all, but I remember my first adventure 28 years ago. My Fighter and another player's Wizard were the only PCs that survived until the pentultimate room, where we both fell in battle to a purple worm. That final battle was epic, and turned on a few key rolls. Neither side pulled punches or fudged rolls either- everything was in the open.
And despite the TPK, that adventure had me hooked for life on this hobby. If I hadn't moved away that summer, I'd have played at that DM's table again in a heartbeat.
So, yes- use the Sea Hag.