"How hard is this?" depends on your skill and character. Hm if I would have to compare it to something. I think of the Base game as pretty laid back and not all that difficult anymore. I went into the DLC with a fresh character which was under leveled too that killed i think only 3 or 4 bosses in the base game. Compared to the base game the bosses and enemies are way more aggressive, and tend to combo quite a number of moves. You can pick up Revered Spirit Ash (to permanently buff your spirit summons within in the DLC) and Scadutree Fragment (to permanently buff your damage reduction and attack damage within the DLC). These help :). For my play style, build and skill level the bosses are quite tough^^. Some stats: haven't managed to kill another boss besides Bayle. He took me 5h of tries, but got dragon priestess waifu as a summon now. Did fight in the beginning a mini-boss in a 1 room crypt I found for 4h. Currently trying to beat the Divine Beast (one if not the first dlc boss) with my flaming fists, which is a terrible idea since the hit box is quite a bit jank on it and fists/fist weapons got no reach :D.