Pretty simple question, but I cant arrive on a solid answer for it
When I cast Neoform sacrificing a Young Pyromancer as a cost, will that Young Pyromancer still trigger? I've been told costs are paid first and the pyromancer is dead before the spell is 'cast'?
No, Young Pyromancer's ability won't trigger here, for the reason you state.
Since you sacrifice Young Pyromancer as you pay Neoform's costs, Young Pyromancer won't be on the battlefield at the moment its ability would trigger (C.R. 601.2h-i).
When I cast Neoform sacrificing a Young Pyromancer as a cost, will that Young Pyromancer still trigger? I've been told costs are paid first and the pyromancer is dead before the spell is 'cast'?
Since you sacrifice Young Pyromancer as you pay Neoform's costs, Young Pyromancer won't be on the battlefield at the moment its ability would trigger (C.R. 601.2h-i).