Above and beyond their similar difficulty levels, Dark Souls and Darkest Dungeon have overlapped in the past by virtue of player-made mods. To this end, Carnifex's Warrior of Sunlight class mod—which recreates Solaire of Astora in Red Hooks' unforgiving cavern crawler—is easily one of the best, and Daoro's Dragonslayer Knight class mod is another that's caught my eye.
By adding Dragonslayer Ornstein to Darkest Dungeon, players get a new religious class whose attacks increase his speed and dodge capabilities. Equipped with his iconic spear—"a weapon of the gods imbued with the strength of lightning"—Ornstein, the boss who teamed up with Executioner Smough in the original Dark Souls, can also harness divine power, at the expense of his stats.
Highlights of Ornstein's abilities include the Charging Stab, which moves him to the front and deals 20 percent more damage, while upping dodge and speed by five and two respectively; and the Nimble Defense, which moves him back and buffs dodge while applying riposte.
My own favourite, however, is the Shocking Impale which is described thusly: "Rank 1 only, Impale the enemy on your swordspear stunning them and dealing 20 percent extra damage, also ignores armor. You lose all your dodge and a lot of speed for 1 turn after using this move. -5 Dodge -2 Speed."
Full details, including installation instructions, on Daoro's Dragonslayer Knight class mod can be found via its corner of Nexus Mods.