This article's content is accurate to the most recent public game version, 0.4.8d.
"[5 Turns] Reduces all Physical damage received by 40%, Acid damage to 0%, but increases Fire damage by 25%."
Cost: 6 MP
Source: Equipping the Slime Princess' Core.
Slime Body is a spell that applies a buff reducing 
Blunt and 
Sharp damage taken by 40%, and gives immunity to 
Acid damage, but increases 
Fire damage taken by 25% for five turns to the user. The spell cannot be cast again to refresh it while it is still active.