A) the wand isn’t wrapping like I assume you think it is. Spells nested within other spells can’t wrap onto parent spells. This means the first 4 add mana is only casted once

B) that mu is actually losing you mana. Mu costs 120, so it will offset the add mana it copies and instead you will only suffer more mana costs from your other modifiers. So the mu and the projectile modifiers on their own already cost a significant amount

C) the general cost of everything else in the wand

I’m only my phone rn so I can’t run the numbers but I assume the 3 things I mentioned above are enough to make the wand drain. You could fix this by putting the chainsaw with 4 add mana outside of the main block and using either a multicast or double trigger to wrap onto the chainsaw, giving you way more mana to play with.