If my memory serves me right, one of them was basically a Giant Harpooning Barnacle, and wasn't there a Harpoon Spider in D&D as well?
Will need to do some reading to check for precedents…
There's a Harpoon Spider in
Monster Manual III, but I couldn't find the harpoon-shooting shellfish.
I think it was in a 3E Adventure I read years ago. I remember the PCs had to go down an underground river that was infested with the things.
Anyhow, the Harpoon Spider has:
Harpooning (Ex): As ranged attacks, a harpoon spider can fire one or two of its fangs up to 20 feet (no range increment). The spider can fire at two different targets if it chooses. A successful hit deals 1d4+1 points of damage as the harpoon hooks the flesh of the target and immediately exudes a thick, sticky glue. The spider can reel in a harpoon as a free action; treat this as a trip attack (+10 bonus) against any creature attached to the fang. Failure indicates that the harpoon rips free (and deals another 1d4+1 points of damage to the victim). Success indicates that the victim is pulled off its feet and dragged back to the spider, who can immediately make a free bite attack against the victim. A harpoon spider can only pull a creature smaller than itself in this manner. Attempts to retract a creature of its own size or larger automatically cause the fang to rip free as if the trip attack failed. The glue exuded by the spider's fangs decomposes quickly, and at the end of the spider's turn the fang automatically detaches.
Another precedent is Planescape's Bonespear, which does not have an official 3E version but is converted in the Creature Catalog with:
Harpoon (Ex): The bonespear's horns have a range of 40 feet (no range increment). If it hits with a spear attack, the spear lodges in the opponent's body and draws the victim 10 feet closer to the bonespear each subsequent round (no attack of opportunity) unless that creature breaks free, which requires a successful Strength check (DC 20) or Escape Artist check (DC 23). The bonespear can draw a creature to within 5 feet of itself and bite with a +4 attack bonus in that round.
A single attack with a slashing weapon that deals at least 10 points of damage severs the spear (horn) (AC 18).
There's also the Harpoon thrown weapon that appears in
Frostburn or
Stormwrack (with identical stats & description) as well as the
Arms & Equipment Guide (a older 3.0 source with a slightly different presentation). The rules are as follows:
Frostburn and Stormwrack
15 gp, 1d10/×2 piercing, 10 lb, 30 ft. range increment
Harpoon: The harpoon is a broad-bladed spear forged with barbs. The shaft of the harpoon has a trailing rope attached to control harpooned opponents. Though designed for hunting whales and other large sea creatures, the harpoon can be used on dry land.
If it deals damage, the harpoon lodges in an opponent who fails a Reflex saving throw (DC 10 + the damage dealt). A harpooned creature moves at only half speed and cannot charge or run. If you control the trailing rope by succeeding on an opposed Strength check while holding it, the harpooned creature can move only within the limits that the rope allows (the trailing rope is 30 feet long). If the harpooned creature attempts to cast a spell, it must succeed on a DC 15 Concentration check or lose the spell.
The harpooned creature can pull the harpoon from its wound if it has two free hands and takes a full-round action to do so, but it deals damage to itself equal to the initial damage the harpoon dealt. A character who succeeds on a DC 15 Heal check can remove a harpoon without further damage.
Arms & Equipment Guide (3.0)
15 gp, 1d10/×2 piercing, 10 lb, 30 ft. range increment
Harpoon: The harpoon is a broad-bladed spear forged with barbs. The shaft of the harpoon has a trailing rope attached to control harpooned opponents. Though designed for hunting whales and other large sea creatures, the harpoon can be used on dry land. Even with the Exotic Weapon Proficiency (harpoon) feat, creatures smaller than Medium-size take a –2 penalty on their attack rolls due to the harpoon's weight and bulk.
If it deals damage, the harpoon lodges in an opponent who fails a Reflex saving throw against a DC equal to 10 + the damage dealt. The harpooned creature moves at only half speed and cannot charge or run. If you control the trailing rope by succeeding at an opposed Strength check while holding it, the harpooned creature can move only within the limits that the rope allows (the trailing rope is 30 feet long). If the harpooned creature attempts to cast a spell, it must succeed on a Concentration check (DC 15) or fail, losing the spell.
The harpooned creature can pull the harpoon from its wound if it has two free hands and it takes a fullround action to do so, but it deals damage to itself equal to the initial damage the harpoon dealt. For example, if you hit with a harpoon and deal 8 points of damage, the target takes another 8 points of damage when it removes the harpoon. A character who succeeds on a Heal check (DC 15) can remove a harpoon without further damage.
So can we use any of that?