[can you deal 70% of HP via implosion, and then buff it to 200%+ of that via Entropic Recurrence on the spot? So basically anything with mech resistance <60% will just insta-die no-matter-what?
No. ER is an end-of-turn DoT, and the damage is smeared pretty wide (it was originally far too powerful and was brought back into the realm of reason - it *used to be possible* to do as you describe, but no longer). Still, if you ER a good heavy Implosion/TK Punch you certainly can put a lethal DoT on the target, then just go run away and let them die off on their own. For one-turn kills, you're still probably better off with a Proxied Implosion on your main target, then maybe a ThermoD from a secondary target or if your main target is alone, use that Proxy again for a TK Punch.
EDIT: Let me make an amendment, here, but leave the original post since I don't hide my mistakes
If you can get a *single* Implosion to do over 50%
(second edit: not 40, 50 - typo) of the target health, and you proxy the Implosion, and ER
that, then the target should die at the end of their following turn, so if you would call that insta-die then absolutely yes, and I was wrong to say no.
OK, I'm tired enough that I'm confusing myself. Basically, ER will kill an enemy after they've taken their turn. It will not apply damage at the end of the turn when you apply it, so if ER is going to kill an enemy they will always get a turn before they die, no matter what. I'm going to take a nap before I confuse anyone else - myself included - any further