Combat
While gricks are incapable of forming large armies and do not have the intelligence to devise complex tactics, much less the ability to wield weapons, they are still cunning and wily combatants capable of harming experienced adventures. A grick ambush is still a terrifying thing in its own right, with up to four gricks capable of attacking a single opponent from a variety of angles.
A character attacked by gricks would do well to bear the grick's strengths and weaknesses in mind and to formulate strategies accordingly.
Strengths
Damage Reduction
The main problem that adventurers face when fighting gricks is that a lot of weapons simply do not inflict much damage on them. Their rubbery bodies, while easy enough to hit, experience no difficulty in turning aside steel. Unless the weapons being used against them are magical, they are all but useless against a grick.
Multiple Attacks
The main threat posed by a grick's offensive abilities is the sheer number and relentlessness of their attacks. A grick's chosen prey can expect to face four tentacle rakes and a bite from its beak every round. An unprotected target can expect to be slashed into pieces within a minute.
Attack from Above
Gricks excel at climbing and could easily hide on the walls and ceilings of caves, lying in wait for a meal. A favourite tactic of gricks when ambushing larger targets is to drop down on them from above. Attacking in this way counts as attacking from higher ground, granting the gricks +1 to attack rolls.
Weaknesses
Fortunately, gricks are not the supreme race of the Depths, and have various disadvantages of which the plucky adventurer can take advantage.
Lack of Fortitude
While they are able to resist weapon damage, gricks have one physical weakness that seems especially fitting. They are not particularly resistant to adverse biological effects such as poisons, diseases and so on. While they can breed fast and are difficult to squash, exterminating them is still fairly easy if you use the right methods.
Poisoning a blade is not a good idea, however. If your weapon is non-magical and you use poison that is dependent upon injury in order to take effect, you run the risk of not harming the grick at all, wasting a dose of expensive poison into the bargain. Worse yet, you may run the risk of poisoning yourself if you're not an assassin or a blackguard
General Advice
Carry Magic Weapons
The single most important thing to bear in mind when hunting gricks is that one should carry magic weapons. It is quite simply the only way of cutting through their rubbery hides efficiently. If no magic weapons are available, then a substitute can be found in the magic weapon and greater magic weapon spells. This of course means that a spellcaster is necessary, and the best kind to have for this purpose is a sorcerer. Given that they can cast magic spontaneously, and are able to cast more spells. Having a few scrolls with such spells scribed upon them is another option, and a rather cost-effective alternative to having the actual weapons at hand.
If magic weapons are unavailable, heavy weapons such as greatswords and greataxes are the next best thing. If the strongest adventurers wield them, they may be able to inflict a little damage upon a grick. If no adventurers are particularly strong, judicious use of divine power, enlarge person or bull's strength spells is advisable.
Dress for Battle
The many attacks of a grick need not be as terrifying as they seem. Any characters that wear heavy armour are likely to be fairly safe from them. The only characters who ought to worry are wizards and sorcerers as they are more prone to attack thanks to their lack of armour. While protective items are particularly useful, spells such as shield or mage armour are readily available to low-level arcane spellcasters and should be used whenever possible.
Prevention is the Better Part of Cure
While killing a grick is the only certain way of making sure it does not cause any problems, it is possible to drive them off without having to draw weapons. It is worth bearing in mind that surface gricks cannot abide bright light. A daylight spell will keep gricks at bay unless they are truly desperate for food.
Take Advantage of their Frailty
An effective anti-grick tactic is to subject them to attacks that require successful Fortitude saves in order to avoid adverse effects. Since Fortitude is the grick's weakest saving throw, they are far more likely to fail the check required of them. Although poisons and diseases can have a devastating effect on gricks, it is perhaps best to deliver them by magic, using poison or contagion spells.
Keep your Eyes Open
While the grick's attack from altitude can be effective, and their stealth skills are top rate, it is always a good idea to make sure that one member of the party has advanced his Spot skill. Foiling their ability to hide themselves takes the element of surprise from the grick, and thus reduces their effectiveness. Furthermore, if an adventurer can win initiative, then it is possible that she could attack and kill the grick while it is attempting to hide on the ceiling or wall, depriving of its ability to attack from a greater height.
Role-Playing with Gricks
Gricks are primarily a nuisance monster. They have little in the way of intelligence, produce nothing, and are largely disorganised. While their behaviour is arguably animalistic, the alien nature of these creatures can be made apparent by playing up their unusual appearance, having truly unwholesome smells issue from their wounds, and paying heed to their peculiar lifecycle. The strangeness of a mind is a difficult thing to portray, especially when dealing with a monster of animal intelligence, but it can be implied by showing how difficult they are to control.
Gricks are stealthy predators, so let them ambush. Consider letting one grick do the majority of the attacks, then have two or three others creep out of nowhere or fall off the ceiling and start their own assault. Make use of flanking attacks, force the PCs to fight on as many fronts as possible, and employ a hit-and-run tactic. Gricks are merciless fighters, but if they are presented with overwhelming odds (most PCs outclass them) they prefer to wear their prey down before moving in for the kill.
Conclusion
It is difficult to demonstrate the strangeness of gricks, and possibly even more difficult to keep your players interested for even a short time for a monster that is so easily dismissed as sword fodder. The simple way around this is to make sure that a reasonable amount of detail is given during grick encounters. Make your flavour text descriptive, perhaps even Lovecraftian. See to it that their lair is established and reachable, and show what they can do to their victims.
Gricks are most commonly encountered when hunting, and should ideally be encountered in conditions of darkness. Their darkvision can then be used to their advantage, since only half-orcs and dwarves will not be dependent upon light sources. Bear their habitats in mind, and work out how they enter cities and towns if such areas fall within their territories. If they are attacking settlements, be sure to foreshadow any encounter with gossip about disappearances, and rumours of how the streets are dangerous at night. Having the locals spread a legend about a night-time murderer who mutilates bodies is one way of grabbing the players' interest while throwing them off the scent slightly, giving the final realisation of the plot a little more shock value.
Running a grick-themed adventure is perhaps the easiest way to make these monsters as interesting as they can be. In most cases, the problem they pose is a simple one: they have a tendency to go where they are not welcome, and there is always likely to be someone who wishes to have them removed. By making sure the gricks are well established within their lair, the task of exterminating them can be made more difficult, requiring them to make use of their brains rather than simply wading in and hacking them to death. The terrain should not favour the PCs.