This is a short EL5 encounter for four 4th-level player characters (PCs). The encounter takes place in a low natural cavern.
The encounter can be placed in any underground area of your campaign world. Ideally, this is a lightly traveled corridor in which some gricks can lie in ambush and wait for prey. As always, feel free to adapt the material presented here as you see fit to make it work with your campaign.
The treasure described below follows the standard guidelines for wealth by encounter level. The gricks presented in this encounter are slightly advanced; yet still remain within the guidelines for a CR3 creature. A party with no access to magical weapons, offensive spells, or damaging alchemical items will find themselves in serious peril. A party so poorly equipped should probably also not be adventuring in dangerous underground areas to begin with!
This natural tunnel has a low ceiling, only about 6 feet high, any large biped navigating the corridor must squeeze down low, suffering a -4 penalty on attack rolls and a -4 penalty to AC. Movement while squeezed is at half speed.
The ground is covered with broken pieces of stalactites, broken rock, and other dense rubble. It costs 2 squares to enter a square with dense rubble. Dense rubble adds 5 to the DC of Balance and Tumble checks, and it adds 2 to the DC of Move Silently checks.
A Spot check (DC 10) reveals bones, scraps of clothing, and pieces of large vermin carapaces mixed in with the rubble on the floor. A Spot check (DC 27) reveals a pair of gricks hiding in small cubbyholes in the ceiling. The gricks are located at each position "G" on the map (see below). (The spot check for the gricks assumes they have taken a 10 on their hide check).
The walls are rough-hewn stone (Climb DC 15). A medium-size creature can brace itself while climbing in the cubbyholes (Climb DC 5). A grick has a natural climb speed and is able to maintain its Dex bonus to AC while climbing above.
Advanced Gricks (2): CR 3; SZ M Aberration; HD 4d8+4; hp 22 each; Init +6; Spd 30 ft., climb 20 ft.; AC 16 (+2 Dex, +4 natural), touch 12, flat-footed 14; BAB/Grap +3/+5; Atk +6 melee (1d4+2 tentacle); Full Atk +6 melee (1d4+2 x4 tentacles) and +0 melee (1d3+1 bite); Space/Reach 5 ft./5 ft.; SQ Damage reduction 10/magic, darkvision 60 ft., scent; AL N; SV Fort +2 (1 base, +1 Con), Ref +3 (1 base, +2 Dex), Will +5 (4 base, +1 Wis); Str 14, Dex 14, Con 12, Int 3, Wis 14, Cha 5.
Skills: Climb +10, Hide +17, Listen +1, Spot +1. Feats: Improved Initiative, Track(b), Weapon Focus (tentacle).
Tactics: The gricks wait until the bulk of the party has passed before attacking. If they have not been spotted, they have a surprise round. They attempt to attack at a time in which both gricks can reach a foe while remaining in their cubbyholes in the ceiling. (A grick can reach into any adjacent square while still hiding in the cubby.) The gricks that remain in the cubbyholes above get a +1 bonus on melee attacks for being on higher ground. The higher ground bonus is not included in the stat block above. If a grick cannot reach a foe, it drops to the floor (as a free action) and scurries to position itself within reach of an opponent. If a grick drops an opponent and is not currently threatened, it picks up the corpse and retreats high into its cubbyhole to feed. If a grick is injured to single-digit hit points, it withdraws to the upper reaches of its cubbyhole and then delays, preparing to attack anyone who tries to climb up after it.
Treasure: Buried amid the rubble on the floor (Search DC 15) is a masterwork throwing axe and a small leather belt-pouch containing 4 tiger-eye agates (10 gp each) and three rose quartz (50 gp each) gemstones. Someone who climbs up into the cubbyholes in search of treasure finds a partial gnome skeleton and a small +1 chain shirt.
Scaling the Encounter: For a level 2 or 3 party, remove one of the gricks and all of the treasure except for the +1 chain shirt. For a level 5-6 party, add two additional gricks and include a wand of magic missile (5th level, 21 charges) with the gnome remains.