Tendril
Boss
What to know
Tendril has 80 health.
It takes extra damage from fire; it resists frost; poison and nonplayer do nothing to it at all. Blunt, slash and pierce land at full damage, so that is what to bring.
It has one attack, 55 blunt.
Of everything craftable, 
Thunderblood Crossbow, 
Lightning Strike and 
Staff of Embers put the most damage through what it resists.
Spawn command
With devcommands enabled, this spawns Tendril in front of you. The third number is the level: 3 spawns a 2-star.
Creature ID: Tendril · all console commands and IDs