The most effective starting strategy for the Inferno faction.

Yes, I also start by getting the old Cerberus upgrade; I think it's the most reasonable option, as in the beginning, we mainly fight neutral creatures in groups of up to 3. We don't really need fire breath at that stage, and the old Cerberuses are twice as good in terms of stats (definitely in terms of damage).

Furthermore, why upgrade Imps? Because their damage is significantly increased. At the beginning of the game, un-upgraded Imps are useless, both for dealing damage and as damage dealers. Therefore, we upgrade Imps first, and last (after Cerberuses), I think we should upgrade Demons, as their main task is to distract. Also, in the early stages of the game, the new upgrade cannot effectively perform the jump attack because if we want to keep them alive, we need to remove the retaliatory attack, and we can only do that when the gates are upgraded, because then we can summon Cerberuses as well, and the number of summoned creatures will be greater.