Genkai Dungeon no Hanshoku Jijou is a Manga/Manhwa/Manhua in english language, MONSTERS series, english chapters have been translated and you can read them here. You are reading chapters on www.mgeko.cc fastest updating comic site. The Summary is

Breed monsters and rebuild the dungeon to defeat the oncoming heroes!
Egin, the master of the dungeon, has been hunted down by the heroes.
To rebuild the dungeon, which now has a 100% chance of reaching the boss's room, he and his second-in-command, Saille, a unicorn in the virgin kitchen, try to breed monsters, but the dungeon is filled with monsters that have their own quirks and quirks...
But the dungeon is filled with monsters that have their own quirks... including a twisted slime who has fallen in love with humans and a shy Dullahan... Will Egin be able to revive the dungeon?