NHF – new heroes for Heroes V 3.1.

Death Knight. The Yeti is number 114. I remember there was also an unused unit in the game, number 89 - the Black Knight.

Isn't the Death Knight number 89? So how many empty slots are there? (how many more units can be added?) If you look at the list of creatures with their assigned numbers, you can see that numbers 90 and 114 are missing.
— Creatures IDs
CREATURE_UNKNOWN = 0 CREATURE_PEASANT = 1 CREATURE_MILITIAMAN = 2; — Conscript CREATURE_ARCHER = 3 CREATURE_MARKSMAN = 4 CREATURE_FOOTMAN = 5 CREATURE_SWORDSMAN = 6; — Squire CREATURE_GRIFFIN = 7 CREATURE_ROYAL_GRIFFIN = 8; — Imperial Griffin CREATURE_PRIEST = 9 CREATURE_CLERIC = 10; — Inquisitor CREATURE_CAVALIER = 11 CREATURE_PALADIN = 12 CREATURE_ANGEL = 13 CREATURE_ARCHANGEL = 14 CREATURE_FAMILIAR = 15 CREATURE_IMP = 16 CREATURE_DEMON = 17; — Horned Demon CREATURE_HORNED_DEMON = 18; — Overseer Demon CREATURE_HELL_HOUND = 19 CREATURE_CERBERI = 20; — Cerberus CREATURE_SUCCUBUS = 21 CREATURE_SUCCUBUS_SUCCUBUS = 22; — Mistress CREATURE_NIGHTMARE = 23; — Hell Charger CREATURE_NIGHTMARE = 24 CREATURE_PIT_FIEND = 25 CREATURE_BALOR = 26; — Pit Lord CREATURE_DEVIL = 27 CREATURE_ARCHDEVIL = 28 CREATURE_SKELETON = 29 CREATURE_SKELETON_ARCHER = 30 CREATURE_WALKING_DEAD = 31; — Zombie CREATURE_ZOMBIE = 32; — Plague Zombie CREATURE_MANES = 33; — Ghost CREATURE_GHOST = 34; — Spectre CREATURE_VAMPIRE = 35 CREATURE_VAMPIRE_LORD = 36 CREATURE_LICH = 37 CREATURE_DEMILICH = 38; — Archlich CREATURE_WIGHT = 39 CREATURE_WRAITH = 40 CREATURE_BONE_DRAGON = 41 CREATURE_SHADOW_DRAGON = 42; — Spectral Dragon CREATURE_PIXIE = 43 CREATURE_SPRITE = 44 CREATURE_BLADE_JUGGLER = 45; — Blade Dancer CREATURE_WAR_DANCER = 46 CREATURE_WOOD_ELF = 47; — Hunter CREATURE_GRAND_ELF = 48; — Master Hunter
CREATURE_DRUID = 49 CREATURE_DRUID_ELDER = 50 CREATURE_UNICORN = 51 CREATURE_WAR_UNICORN = 52; — Silver CREATURE_TREANT = 53 CREATURE_TREANT_GUARDIAN = 54; — Ancient Treant CREATURE_GREEN_DRAGON = 55 CREATURE_GOLD_DRAGON = 56 CREATURE_GREMLIN = 57 CREATURE_MASTER_GREMLIN = 58 CREATURE_STONE_GARGOYLE = 59 CREATURE_OBSIDIAN_GARGOYLE = 60 CREATURE_IRON_GOLEM = 61 CREATURE_STEEL_GOLEM = 62 CREATURE_MAGE = 63 CREATURE_ARCH_MAGE = 64 CREATURE_GENIE = 65; — Djinn CREATURE_MASTER_GENIE = 66; — Djinn Sultan CREATURE_RAKSHASA = 67 CREATURE_RAKSHASA_RUKH = 68 CREATURE_GIANT = 69; — Colossus CREATURE_TITAN = 70 CREATURE_SCOUT = 71 CREATURE_ASSASSIN = 72 CREATURE_WITCH = 73 CREATURE_BLOOD_WITCH = 74 CREATURE_MINOTAUR = 75 CREATURE_MINOTAUR_KING = 76 CREATURE_RIDER = 77 CREATURE_RAVAGER = 78 CREATURE_HYDRA = 79 CREATURE_CHAOS_HYDRA = 80 CREATURE_MATRON = 81 CREATURE_MATRIARCH = 82 CREATURE_DEEP_DRAGON = 83 CREATURE_BLACK_DRAGON = 84 CREATURE_FIRE_ELEMENTAL = 85 CREATURE_WATER_ELEMENTAL = 86 CREATURE_EARTH_ELEMENTAL = 87 CREATURE_AIR_ELEMENTAL = 88 CREATURE_BLACK_KNIGHT = 89 CREATURE_PHOENIX = 91 ===================================================================== HAMMERS OF FATE CREATURES ===================================================================== CREATURE_DEFENDER = 92 CREATURE_STOUT_DEFENDER = 93 CREATURE_AXE_FIGHTER = 94 CREATURE_AXE_THROWER = 95 CREATURE_BEAR_RIDER = 96 CREATURE_BLACKBEAR_RIDER = 97 CREATURE_BROWLER = 98
CREATURE_BERSERKER = 99 CREATURE_RUNE_MAGE = 100 CREATURE_FLAME_MAGE = 101 CREATURE_THANE = 102 CREATURE_WARLORD = 103 CREATURE_FIRE_DRAGON = 104 CREATURE_MAGMA_DRAGON = 105 CREATURE_LANDLORD = 106; — Enforcer CREATURE_LONGBOWMAN = 107; — Crossbowman CREATURE_VINDICATOR = 108 CREATURE_BATTLE_GRIFFIN = 109 CREATURE_ZEALOT = 110 CREATURE_CHAMPION = 111 CREATURE_SERAPH = 112; — Fallen Angel CREATURE_WOLF = 113 CREATURE_MANTICORE = 115 CREATURE_MUMMY = 116 CREATURES_COUNT = 117