What works with Summon Phantasm on Kill Support?

I recently started playing a necro soulwrest build, and i'm not to sure which support gems to use with soulwrest. Does anyone know of which gems that work with summon phantasm on kill and maybe which ones would be best?

It's a piercing phys spell, as the skill description says. The necessary links are GMP, phantasm on kill (gives ~10 extra phantasms), minion damage, and faster proj, (faster proj makes the minions a million times better) and i also run pierce for clearing the screen. If youre running solar guards, added fire works really well with your curses/EE, or if you have lightning vaal advocates phys to lightning is also really good. Controlled destruction is also obviously really good.

Btw, 6 linking the staff wasnt necessary

So i six linked my staff because i thought it needed to be six linked. Thankfully i only six linked it in 18 fusings. But why use pierce though? When the gem says it has "a piercing projectile".