I think we should drop the acid spray from the GBB, but otherwise Cleon's probably right about the larva.
The acid I was referring to was not the GBB's acid spray, but that injected by the larvae's bite:
Their mandibles inflict 1-8 hp damage and inject an acidic substance that liquifies the prey’s body. Victims of a giant diving beetle larva’s bite must save vs. poison or suffer an additional 1-6 hp damage.
Making the suggested adjustments to the GBB we've currently got:
Diving Beetle Larva, Giant
Medium Vermin (Aquatic)
Hit Dice: 2d8+4 (13 hp)
Initiative: +0
Speed: 20 ft. (4 squares), swim 20 ft.
Armor Class: 15 (+5 natural), touch 10, flat-footed 15
Base Attack/Grapple: +1/+2
Attack: Bite +2 melee (1d8+1 plus 1d6 acid)
Full Attack: Bite +2 melee (1d8+1 plus 1d6 acid)
Space/Reach: 5 ft./5 ft.
Special Attacks: Acid, improved grab
Special Qualities: Darkvision 60 ft., jet, vermin traits
Saves: Fort +4, Ref +3, Will +0
Abilities: Str 13, Dex 10, Con 14, Int 0, Wis 10, Cha 9
Skills: — [
racial bonus on Hide?]
Feats: —
Environment: Temperate or warm freshwater
Organization: Solitary or cluster () ?
Challenge Rating: 1 ?
Alignment: Always neutral
Advancement: 3-4 HD (Medium); 5–6 HD (Large)
I dropped the Challenge Rating from the GBB's CR2, since the larvae aren't that nasty.
It's a lurk-and-ambush hunter, so could do with a racial bonus on Hide so its prey don't spot it before wandering close enough for it to attack them.
The acid is a cocktail of digestive enzymes, so we should probably specify it only harms organic creatures.
Upon reflection, the jet could be faster than 120 ft. 120 ft. is the equivalent of a Run action by a creature with a 30 ft. swim speed, it may be too slow for it to effectively flee from predators. Shall we go for 150 ft. or 200 ft. instead?
