I have been struggling with this myself, to find a good grenade to proc Vampyr.
I have tried Ghast Call (I have the basic version) and it seems to work ok. Its better when you are under the influence of terror because the grenade will then spawn more skulls. But the problem with that is to have some gear that gives you terror after skill end, which is tedious because of how the action skill works.
I have tried the purple Torgue Clusterf*uck grenade. Mine spawns 6 mirvs on impact which each then spawns 3 more mirvs, for a total number of 25 explosions (1 on impact, then 6 mirvs, then 18 mirvs). It seems to work better than the Ghast Call, but still not all that great. At least you dont have to jump in and out of Iron Bear every time to get the full effect. BUT it causes major frame drops for me
I just got the Tracker (cloning, 3 mirv, 30% heal) from a vending machine. I have not tried it yet, but people seem to like it so I will give it a try.
The Surge, has too much spread on the explosions for my liking. But maybe I need to test it some more to get the hang of it.
Tiny Tinas Hopper, I find, has too few explosions .
Quasar, Storm Front, Hex does not work with Vampyr.
I wish Moze just gets a rework on her skills so we can have som healing in all her skill trees. I would like to go down BM and SoR and still be able to heal myself, without having a synergi with Transformer shield and shock.
Any tips on BM and SoR builds with good sustainability would be very, very appreciated