What Lies Beneath

So, I love Veins Of The Earth. Who doesn't? It's stupid good! Anyway, I wanted to make some beasties to inhabit my own underground terror tunnels, and it would be nice for other people to have them too.

Rock Squid

Sometimes called a "rocktopus" by people who think they are being clever. This is a colossal cephalopod which has adapted to live in caverns. It is about the same size as a giant squid, having a body of about three meters, and limbs five meters long. It has not lost its ancestral ability to swim in aquifers or underground streams deep in the earth, but is equally likely to be found awaiting prey, its invertebrate form compressed into the smallest of spaces. Interestingly it also retains much of the camouflaging ability of its smaller aquatic cousins.

Rules Malarkey

HD 5

AC as Leather

Attacks #4 (Tentacle 1d6, Beak 1d10) or Special (see below)

Movement as humanoid (doubled when in water)

Special Abilities

Compressible: The Rock Squid is able to squeeze through any gap at least 30 cm (1') square and hide the entirely of itself inside a space 1 m cubed (3 cubic feet)

Camouflage: The natural chameleonic abilities of the Rock Squid allow it to hide in plain sight, such as pressed onto a wall. If unmoving the Squid counts as being invisible for rules purposes, although it can be detected by mundane means. 

Aquatic: The Rock Squid has no need to breathe when underwater, and doubles its movement speed when fully immersed.

Spiderclimb: The Rock Squid scrambles over cave walls with powerful suckers, and can move as easily on ceilings and walls as along floors.

Grappling Expert: When the Rock Squid is Grappling, it may devote additional attacks onto one target up to its maximum number. Every additional attack counts as if there was an additional Rock Squid assisting in the grapple. Any successfully grappled character takes an automatic hit from the Rock Squid's Beak.

Treasure: A cloak made of the hide of the Rock Squid will allow the wearer to utilize the Rock Squid's camouflage ability

Iron Weta

Unlike many of the other creatures of the depths, the Iron Weta is not naturally aggressive. About the size of a small cow, it is the natural prey of other creatures of the deeps. It survives by leeching nutrients and minerals from the rocks. Its chitinous hide is formed of carbon compounds and is harder than steel. Although not agressive, it is quite strong and will often attempt to bullrush those it regards as a threat. The best idea is to approach them gingerly, or not at all.

Like this, but big

Rules Malarkey

HD 4

AC as Plate

Attacks #1 (Bite 1d6) and Special (see below)

Movement as cow

Special Abilities

Bull Rush: If the Iron Weta has space to charge, it performs a much more devastating trample. As long as the Iron Weta can move in a straight line towards its target (including if it backs off and then charges forwards again) it increases its bonus to hit by +4, and its damage increases to 1d8. The target also must pass a strength test or be knocked to the floor.

Ferrophage: The Iron Weta, if attacking, will deal an automatic 1d4 damage directly to armour and equipment made of metal. Each point of this damage will destroy one point of AC of armour, or one encumbrance point of metallic equipment. Additionally, outside of combat, the Iron Weta will ingest one encumbrance point of  metal every round if it can reach it. Equipment made of bone, hide, or other non-metallic substance is unaffected.

Treasure: Armour or equipment made from an Iron Weta's carapace is proof against the Weta's Ferrophage ability as well as all other corrosive compounds.

Achromites

Sort of a cross between a termite and a scorpion. Also, about as big as a mountain lion. They spray corrosive venom, and their blood is acidic (I'm not plagiarizing! You're plagiarizing!). Inhabiting underground warrens burrowed out of the living rock, their nests (whilst vigorously defended) are a boon to the brave treasure hunter, as their spoil piles are often filled with gold and gems (which their venom will not destroy). It is best to be wary if spotting a creature far from its nest, as Achromites seldom hunt alone.

Ok, I am plagiarizing a little

Rules Malarkey

HD 2

AC as Chain

Attacks #2 (Claw 1d6, Tail 1d8 save against poison)

Movement double that of humanoid

Special Abilities

Acid Spray: Once per combat the Achromite can spray acid for 1d6 damage (save against blast in order to avoid). On a roll of 6 1 point of armour on the target is destroyed by the corrosive effect.

Acid For Blood: If maximum damage is rolled against the Achromite, the creature that did the damage takes 1 point of damage as a spatter of acid blood hits them. Additionally, when the Achromite dies it bursts apart in a gush of corrosive fluid drenching all creatures in direct contact for 1d8 damage.

Poison Sting: The tail of the Achromite has a poison sting intended to immobilize prey that it might be dragged back to the nest to be devoured alive. Any character stung by the Achromite's tail must make a save against poison or be stunned for 1d6 rounds (on a six they are stunned for an hour).

Treasure: The respect gained from having a body decorated with acid-scars