It depends on the pack/item, if you tell me for which I'll let you know
That must be Cursed Shield
which by default gains multicast. In general on endless you want to start stacking multicast with Lost Fragment and/or Nature's Call
As for Blazing Bull specifically, a Fire Orb would do also cause it to trigger multiple times
Other than that, Moon Essence with Moonveil
, Goblin Essence with Wrench and so on.