this list only has the ones needed for each zone's 100%. the 'world boss' champions will be covered elsewhere, if anyone wants them.
Solomon Island:
Kingsmouth:
Savage Fathom: level 15 deep one, circles the giant tentacle near 910, 160. former nightmare deep one area near journey's end
Night Shift Supervisor: level 15 zombie miner. 824, 670 inside the warehouse at the airport.
Scrap Golem Cremator: level 14 scrap golem. 684, 733. just inside fence at scrap yard.
Surf Nasty: level 12 zombie hulk. wanders near 50, 983 in the water northwest of priest island.
Fire Chief McCaffrey: level 9 zombie fireman. 478, 516 upstairs in the firehouse.
Faithful Husband: level 10 zombie. 725, 397 behind the bed and breakfast
Feigr Jotun: level 8 draug warmonger. wanders near 595, 175
Folr Jotun: level 13 draug lord. wanders near 578, 961 just northwest of airport.
Mr Freezie: level 10 zombie. wanders near 366, 503 just east of priest house (near final revenant feather)
Dunwich Road Horror: level 15 mud golem. wanders large circle between 700, 600 to 888, 541 (south of dunwich road)
Suzie: level 8 zombie. 398, 323 behind the counter in her namesake diner
Father Appleby: level 7 cultist zombie. in cave at 386, 21
Unearthed Rubble: level 14 mud golem. 682, 687 outside scrapyard. must interact (f) to activate
Fallen Thane: level 13 norse zombie. 578, 812 inside crater on hill.
Feigr Invasion Commander: level 10 draug lord. 600, 300 on boat
Dumpster Diver: level 4 zombie hulk. 293, 232 behind sycoil gas station
Lord Bittern: level 11 zombie. 268, 528 in fenced in area in graveyard behind church
Forgotten Fiend: level 6 zombie. grave at 279, 26
The Reawakened: level 7 cultist zombie. wanders water near 560, 33 south of zombie cultist area
Solomon's Omen: level 12 zombie bear. 37, 846. southwest of southwestern priest island
Nattfari: level 13 norse zombie. circling hill at 578, 812
Travelers Torment: level 6 wisp. circles near 261, 121 near wisp tree
Savage Coast:
Coach Roarke: level 19 zombie. kicking a tree at 490, 194
The Collector: level 15 chainsaw scarecrow. at 588, 683 on cliffside. 702,609 is start of path to reach.
The Marooned Oarsman: level 15 draug warmonger. wanders near 987, 951 near northern map edge.
Svell Queen: level 19 draug queen. circles a pool at 255, 248 at base of cliffs near lighthouse
Unrequited: level 19 zombie. cliffside at 874, 328
The Headmistress: level 20 ghost. 302, 383 second floor of academy
Blackchaff: level 17 shotgun scarecrow. inside barn at 503, 566
Ashen Son: level 19 draug warmonger. 392, 107 house on cliffside
Svell Berzerker: level 19 draug warmonger. wanders near 921, 526 in frenchman's cove
Lab Meat: level 18 flesh golem in crater at 540, 180 (former nightmare area)
The Sleeping One: level 16 wendigo in or near cave at 289, 896
Umbral Brood King: level 16 ak'ab. circles loms treehouse near 492, 896
Lurking Revenant: level 15 revenant. flock of crows at 431, 814 next to slimy mass (ak'ab side mission behind black house)
Sycoil Attendant: level 16 zombie. 342, 743 at front of gas station
Umbral Brood Royal Guard: level 16 ak'ab. against a cliff at 447, 1006
Tidal Leader: level 22 draug warmonger. in front of boat at 76, 773
Rift Rancour: level 15 incubus. stands on rock at 865, 880
Byblos, Zombie Janitor: level 20 cultist zombie. 284, 355 academy attic guarding 'hexes' book
Tolba's Bane: level 23 deep one. hillside at 35, 858
Clyde & Bonnie: level 19 doll scarecrow. activates when approached at 870, 410 on cliffside
Svell Lord; level 19 draug lord inside smuggler's scar cave at 905, 618
Henderson's Horrors: three different scarecrows (one of each weapon type) that circle around 192, 579, the blue fires. level 22
Innsmouth Track Captain: level 17 running zombie. huge circle north of the academy. easily found around 287, 539 near creek
Necrotic Mutation: level 19 filth hulk. next to filth barrels (side mission) at 699, 127
Blue Mountain:
Hrapp, Fog Cloaked: level 25 draug lord at base of cliff at 621, 547 in quarry
Algernon: level 27 wendigo. 666, 442 spawned by jumping on burrow near cliffwalker
Spinecrusher: level 28 draug warmonger on cliffside at 168, 895
Abyssal Captain: level 23 briny zombie. spit of land at 56, 180
Scarlet Conductor: level 24 wraith wandering near 394, 505 in ash forest (also can spawn in cabin during freeborn mission)
Tourist Guide: level 27 'sleeping' zombie. 325, 661 just inside wabanaki village. can wake up by approaching
Contaminated Quarry Mutation: level 26 filth hulk wandering near 517, 369
Gorestreak Alpha: level 28 wendigo circling at 343, 644 in wabanaki village
Sorrow Harbinger: level 28 revenant at 440, 932 beneath a tree
Bastard of the Brine: level 28 deep one. 191, 844 just south of agartha entrance
Billy's Muse: level 25 'spider' shade wandering southern moon bog near 871, 459
Penumbral Elevated Caste: level 27 ak'ab at 810, 23 past a walkway bridge
Mutated Corpse: level 29 flesh golem at 187, 752 in wabanaki graveyard
Pestilent Revenant: level 27 crossbow revenant with two spawn points. both 256, 556 and 577, 361 (one near the ursine horror, the other in a building near festering foreman)
Undying Postman: level 29 sleeping zombie at road leading to wabanaki camp. 121, 427
Nubilous Brood Prince: level 23 ak'ab spawned by destroying royal burrow at 588, 98
Stone Envoy: level 26 concrete golem 'sleeping' at 459, 359, cliffside
Rusted Machinery: level 24 scrap golem wandering near 512, 578 outside blue ridge mine
Vetr Berserker: level 25 draug warmonger. at 962, 941
Festering Foreman: level 26 zombie hulk at 592, 362