Growth has 100 health and spawns in the plains.
It takes extra damage from blunt and fire; it resists slash, pierce and frost; poison does nothing to it at all.
It has one attack, 50 poison and 45 blunt.
Some of what it throws is elemental, so poison resistance is worth having.
Of everything craftable, 
Thunderblood Sledge, 
Frostfire Sledge and 
Staff of Embers put the most damage through what it resists.
It always drops 
Tar.
Growth is an undead blob that sits in the tar pits of the Plains. It has 100 health, is weak to blunt and fire, resists slash, pierce and frost, and is immune to poison. Unlike the other blobs it fights at range, launching six tar orbs every 8 seconds from up to 15 meters for 45 blunt and 50 poison, applying both Tarred and Poison. Each kill gives 1 Tar and a 10% chance of a 
Growth Trophy.
The Tarred debuff wrecks your attack and movement speed, so fight them from outside the pit with a bow and never brawl in the tar itself. Blunt, fire and frost work; slash and pierce mostly annoy them. Plains wildlife hates them too, and a lox herd will happily do your tar mining security.
With devcommands enabled, this spawns Growth in front of you. The third number is the level: 3 spawns a 2-star.
Creature ID: BlobTar · all console commands and IDs