(open in new tab if it doesn't play) As you can see in the video, while seduced by the left hand, I was hit off of the rope by the left hand's Mana burn attack for -3000MP, causing me to have 0MP remaining. My Endure is level 20, which means I gain +30MP every 10s. I gained that 30MP right after I was hit off of the rope. When my character reached the legs, I used Hero's Will (which costs 30MP to activate) but it did not work. My MP went from 30MP to 0 and immediately back to 30MP. Since Hero's Will didn't work, the first seduce caused me to activate the right hand's seduce (the point where I start jumping). I really should've been spamming Hero's Will during the second seduce, but it all happened too fast and I was too busy panicking at why it didn't work that first time. I don't think this is an intended feature of seduce, but I also am not too sure if this is even fixable. edit: It seems like the exact source of the problem is having the exact amount of MP left to cast a skill, not seduce affecting passive mp gain.
Seems the underlying reason for this is the following: Having the exact MP to cast a skill once (eg. you have 20 mp and cast triple throw which costs 20mp) will make the skill animation play out but will deal no damage and provide no buff. Triple throw Haste Flash jump still works until you recover enough MP you no longer have exactly 13MP. Then you will have to recover MP to cast it again. So in the above, having exactly 30MP allowed Hero's Will to be cast but made the skill do nothing.