It sounds like you're trying to dot and then shadowbolt.

So just a macro like this:

/castsequence [nochanneling, talent:1/3, talent:2/1/2] reset=target/combat Agony, Corruption, Unstable Affliction, Unstable Affliction, Unstable Affliction, Deathbolt, Agony, Corruption, Shadow Bolt, Shadow Bolt, Shadow Bolt, Agony, Corruption, Shadow Bolt, Shadow Bolt, Shadow Bolt

The talent selection lets you choose which rotation to use based on the talents and you can see it applies dots, several UAs and finally deathbolt before it goes into a non-deathbolt rotation (because deathbolt has a 30 second cooldown).

It will reset on target, which may not work very well within 30 seconds. You can change that up however you like. I highly, highly recommend using GS vanilla (not GSE) because you can put all your macros in a single file and use notepad++ to edit them which is visually better than the WoW macro window.