The first point you made is true, you do not require the second you just need to use mana so you dont have 65 mana to use before the walking bomb does damage, however i find two energy barrages to do very high damage.
Fair enough, but the video makes it seem like you
have to have Flashpoint
and get the second Energy Barrage off or this won't work. Clearly, that's not the case, but the video makes it seem like it.
Also that only spell i have found that also works like this how your mana gets taken from you once it causes damage is Flashfire from the inferno tree however the damage for this will occur in a quicker space of time that walking bomb so you need to be even quicker and preferably further away when using Flashfire
Since Flashfire is considered a sub-par spell, I'd say that makes the title of this thread misleading. After all, the only specialization that can make use of this is the Necromancer, while the title implies that any mage can pull this off.