D&D 5E I'm playing D&D tonight. Tell me what should happen

[bedir than]

My work D&D group meets every other Wednesday evening, for just an hour. They've fought many crawling claws, a ghost, an invisible spector and a few other things. I didn't level them up yet. Ooops. They're level 1. The four characters should probably be nearly 3rd.

They just unlocked a puzzle to enter a hallway towards a Vampire Spawn in what would be their first big bad, but who is actually a herald (the Slyflourish) concept of a much larger problem of undead returning to the city.

Should they fight it, even though they are underpowered? (We'll only have 3 tonight)
Should it be a herald and try to flee out the other exit?

Hit me up with inspiring ideas

 

[Knorrrssk]

Personally I would have it pull it's punches a bit; reduce the damage it's outputting since it doesn't really see them as enough of a credible threat for it to bother. Let them fight it for a while, then when it bores of their company it slaps one of them really hard and leaves.

 

[Tutara]

I mean, the first thing they should do is level up! Faced with their first serious foe, they draw deep on their selves to rise to the challenge. Or some such.

I worry smacking underlevelled characters with a CR 5 beastie might end up as an anti-climax, particularly if you yourself recognise that they should be further along the levels than they are.

 

[aco175]

I would let them level to 2nd level, thinking it only takes 5 minutes out of the hour you get to play. You could have a NPC escort them from the town guard or such and have him totally killed by the spawn like in the movies. "I think the problem is on the other side of this doo- Augh." The players get to see some power of the spawn and can decide to fight or flee from there.

 

[Voadam]

I mean, the first thing they should do is level up! Faced with their first serious foe, they draw deep on their selves to rise to the challenge. Or some such.

Go full anime. Have dark theme music play when they first enter combat with the villain. After the villain makes his first attack and it is the player's turn, play different stirring high tempo music and in the middle of combat have them level up.

Going to second is mostly one new HD and a new power or spell slot for most classes and not a subclass choice, so it can be done quickly on the spot.

A vampire spawn is a serious opponent however that I would expect to crush three second level PCs if played tactically and all out, even if they are paladins and clerics. 82 hit points, resistance to non-magical weapons, regeneration 10, and multiattack is a lot.

I would have him make a big speech, fight and show he's a serious opponent, but be driven off when wounded well before he is close to death as he does a villain withdrawal, a last speech to threaten about the oncoming undead problems, and then escape using spider climb.

 

[iserith]

Telegraph the creature's level of power relative to the PCs and its intentions or motivations, including ideal, bond, and flaw, then have it engage in social interaction.

Let it play out and decide what to do in the moment, based on how the players decide to approach the situation. If despite your forewarnings they decide to engage it in combat, then let the chips fall where they may.

 

[bedir than]

I didn't give much of the setup.

They were in a room with a puzzle activated secret door. One of them got cautious. They reclosed the door, holing up for the night. There was a minor fight (2 rounds). They long rested. They leveled. They are now re-chasing the spawn, who will probably try to recruit the wizard who chose to be a necromancer