Bloodthirst Slot by Hacksaw Gaming

Four monsters run the paytable here - a green Ghoul, blue Vampire, red-brown Werewolf, and red Demon - and when four of the same land stacked on a single reel, that reel converts into a Monster Reel. The reel fills entirely with the creature and pays a fixed bonus on top of normal line wins: 5x for Ghouls, scaling up to 20x for Demons. Get all five reels showing the same Monster Reel on a single spin and individual prizes get replaced by a Monster Takeover payout. Ghoul Takeover is 100x. Demon Takeover is 2,500x. The symbols themselves look almost hand-painted against stone-carved reel frames and a foggy Transylvanian backdrop, with card values chiseled into stone tablets as low pays.

Standard paytable hits are thin. Demon and Werewolf top out at 10x for five of a kind, Ghouls and Vampires at 6x. The 100x Immortals buy option gets you 10 free spins where one randomly selected monster is the only one that forms Monster Reels - but here, every reel that activates gets permanently marked and shows a Monster Reel on every remaining spin. An Upgrader scatter promotes that monster to the next tier (Ghoul to Vampire, Vampire to Werewolf, and so on), and all marked reels upgrade with it. The cheaper Bloodthirst bonus at 100x also runs 10 spins, just with better reel weights and no marking system. BonusHunt mode at 3x per spin bumps the natural trigger rate fivefold without guaranteeing anything.

The Immortals round is where the game's ceiling lives. Mark three or four reels early, land an Upgrader or two, and suddenly you've got Werewolf-tier Monster Reels (15x each) firing on every spin for the rest of the round. Push that to Demons at 20x per reel across four marked positions and it's 80x per spin before line wins even count. That snowball from a 5x Ghoul start to a full Demon board is mathematically possible at about 1 in 4 million spins - but the partial versions of that sequence, two reels marked with one upgrade, are where most of the decent payouts actually come from.