idk how he did it but for me it came from three things. 1 the machine in the basement which just produces a substance (for a while ive been wondering if it was a trapped monster or the whole building is). 2 the mystery pills that obviously have not given the effect the protag believes they do and come from a person who does not have her interests in mind. 3 the landlord. two reasons with him. first the one i find stranger which is the mirror scene where he said he cant really bare to look at himself (could come off as self hate but having a monster basement makes me feel differently). Then the part where he cant sleep well, which seems minor but when getting jerked off helps him like the basement creature i think a little differently