First off, let me remind you that this bug/exploit will most certainly get fixed very soon, as this bug/exploit allows massive damage to some enemy types.

Max rank Energy Vampire + Max Focus.

Base level 50 enemy:

    • Charger: 2-3 casts will kill them
    • Runner/Leaper: 1-2 casts

now for the actual problematic part of this extra damage. for some odd reason, the Eris Infested boss Phorid can be killed in as little as ONE cast of Energy Vampire, the most you will need is 2. for whatever reason Phorid, although having a very large pool of health and some armor, it seems to take the same damage calculations as a runner, the first pulse of EV taking away at least 1/3 of it's health. And the entire time during this duration it is stunned and cannot fight back. 

This bug does NOT affect Grineer or corpus, but seems to do more to corpus, further proving that whatever damage calculations for EV exist they are affected by armor scaling. furthermore, the higher level the enemy is, the more EV seems to take. Ancients recieve normal calculations and one at the same level as phorid would take significantly more to kill them. 

If you do not believe me for yourself, have yourself or a contact have a max rank EV with a max Focus mod and go to phorid and cast it without shooting a single bullet.