Moat house near Hommlet.

Juvenile                11d8 medium +22 proficiency modifier +2

HP 72.  BW 9d6(32)

Damage modifier +2

bite 1d10

AC 16.                 CR4

Sorcerer level 3   Spell save DC 12; spell attack modifier +4

Cantrips  acid splash, Mage hand, minor illusion, blade ward

Known spells 4

1st 4 magic missile, shield, Charm Person wis save adv

2nd 2 invisibility 

The dragon can be heard with a DC 15 Perception Check (hearing) from well outside where it is, rooting thought the dungeon entrance, it has only just arrived and it has cleared the top level, except for the frogs outside.  

The dragon will make a perception attempt +4, or be surprised.  It will lead with acid, and will use the shield spell at first attack.  Attempt to Charm the ranger, "Protect me!" which should cause some personal muddying of the waters.  It will use Magic Missile twice with 1st spell slot to target the strongest fighters so far, twinned with sorcery.  it will cast Magic Missile once with a 2nd spell slot with four darts.  It will use invisibility to escape, but will return and use its breath weapon and fight to the death.  Hunter's mark will betray this.