The grick is a grayish, subterranean snake-worm monstrosity 5 to 8 feet in length, with a sharp, beaked mouth ringed by four clawed, suckered tentacles—in short, the stuff of nightmares. Normally a cavern-dweller, it occasionally ventures aboveground if food is scarce, ensconcing itself in rocky crevices where prey is likely to pass by.
Its Strength and Dexterity are high, in contrast with its average Constitution, so its preferred method of attack is ambush. It’s also primarily nocturnal, on the basis of its darkvision, though not exclusively: it may, for instance, hide in a dark crevice aboveground, yet attack creatures that are outside in the light. At the same time, though, it’s probably more likely to attack around dusk than in the middle of the day. Although it has no Stealth skill per se, it has the Stone Camouflage feature, which gives it advantage on Dexterity (Stealth) checks in rocky terrain. Consequently, it will stick to this kind of area and remain hidden until a target creature draws near, then Attack from hiding, with advantage.
The grick has Multiattack, but it’s a limited Multiattack: it only gets to make its beak attack after a successful tentacle attack. In other words, it’s gotta grab you before it can bite you. The larger and much tougher grick alpha has a more complex Multiattack: in addition to its tentacle attack, it can also lash out with its tail. It, too, has to hit with its tentacles in order to attack with its beak, however.
Both the grick and the grick alpha, inexplicably, have resistance to physical damage from nonmagical weapons. Nothing in the Monster Manual flavor text suggests why this should be so. It just is. The only conclusion I can draw from this is that the grick is a persistent predator that won’t be deterred by fighting back with ordinary weapons. Only elemental damage or a magical weapon will impel it to back off. However, thanks to its high Wisdom score, which implies a strong self-preservation impulse, it doesn’t take much magical or elemental damage to make it back off, just enough to moderately wound it (9 hp or more magical or elemental damage for a grick, 23 hp or more for a grick alpha).
A grick has a normal movement speed of 30 feet and a climbing speed of 30 feet. The normal movement speed isn’t enough to allow it to hide again once it’s revealed its position by attacking. The climbing speed might be, if it can reach a crevice it can slither into, but there’s a problem with using this tactically, which is that its opponent, upon seeing it slither into that crevice, can simply back well away from it and keep his or her distance, so that the grick has no way of successfully ambushing it again. So I’d say it won’t even try. Once it’s blown its cover, so to speak, it’s committed to melee combat until it prevails or is forced to retreat.
Finally, a grick that renders its opponent unconscious will normally try to carry it back to its lair to devour, by wrapping its tentacles around it and dragging it off. Aboveground, however, that “lair” will often be a crevice that the victim doesn’t fit into. In such a case, the grick has a lot farther to go: it will head for a cave, perhaps, or a burrow, or simply an out-of-the-way spot in the woods where it can find some measure of camouflage. But it won’t stick around and keep fighting just for the sake of fighting. It kills to eat, so if it’s got something it can eat, it will want to go off and eat it in peace.
Next: The people in your neighborhood.