The harpsivell is a tough desert creature that has developed a very strange adaptation: strings line a ridge on its back, and it vibrates those strings to create weird, atonal sounds that disorient or incapacitate both predators and prey. These omnivorous creatures won't eat anything larger than a rabbit, but their sheer size (about 15 feet tall) and relatively flighty nature can make them dangerous.
They are also extremely sensitive to the presence of other creatures, apparently detecting extremely subtle variations of air pressure on their strings.
I think I'm going to base this on the banshee, a creature with minimal extra abilities besides its weird ones.
I'll remove its various resistances and immunities in favor of a more powerful kick (which will replace the banshee's corrupting touch). I actually really like the banshee's detect life ability and will keep that, but powered down to a half-mile radius instead of 5 miles (!).
OK, let's do this!
Homebrewery stat block:
Large beast, unaligned
- Armor Class 12
- Hit Points 60 (10d10+5)
- Speed 40 ft.
STR DEX CON INT WIS CHA 14 (+2) 14 (+2) 10 (+0) 12 (+1) 11 (+0) 11 (+0)
- Saving Throws WIS +3
- Senses Darkvision 60 ft., Passive Perception 10
- Languages --
- Challenge 4 (1,100 XP)
Detect Life. The harpsivell can magically sense the presence of creatures up to half a mile away that aren't undead or constructs. It knows the general direction they're in but not their exact locations.
Kick. Melee Weapon Attack: +4 to hit, reach 10 ft., one target. Hit 14 (3d6 + 4) slashing damage, and the target must make a DC 13 Constitution saving throw or be knocked back 5 feet and fall prone.
Weird Music. Each creature within 60 feet of the harpsivell that can hear it must succeed on a DC 13 Wisdom saving throw or be frightened for 1 minute. A frightened target can repeat the saving throw at the end of each of its turns, with disadvantage if the harpsivell is within hearing distance, ending the effect on itself on a success. If a target's saving throw is successful or the effect ends for it, the target is immune to the harpsivell's Weird Music for the next 24 hours.
Tone of Discord (1/day). All creatures within 30 feet of the harpsivell that can hear it must make a DC 13 Constitution saving throw. On a failure, the creature drops to 0 hit points. On a success, the target takes 10 (3d6) psychic damage.