Earliest examples of bosses with more than one "phase"
One thing I really notice when playing early NES games is that most of the bosses, even the final boss, often only have one phase, making them seem a bit underwhelming and unsophisticated. The thing that made me think of this topic was encountering Ganon in the original Legend of Zelda. 4 hits, 1 silver arrow, goodnight.
I think the moment developers realized it would be super badass to give their final boss or their late stage boss a second, stronger phase after their life has been depleted was a real kick in the teeth to the gaming industry that persists to this day.
So what were the first ever or earliest games to ever implement this? I have 2 (now 3) that come to mind. Please let me know the earliest that come to mind for you either and if there's any earlier than these.
Jacquio - Ninja Gaiden (1988)
Dr. Wily - Mega Man (1987)
Dracula - Castlevania (1986) (1987 in the US though)
When I started writing this post, Wily was the earliest I knew of. (And then I remembered Dracula) Deplete Wily's life bar at the end of the game, and he sprouts a second life bar with very slight modifications to his flying vehicle. Now you can see his head peeking out from the damaged windshield, now his light blasts come at you in big circular patterns instead of straight on. And also you might need to switch to a different weapon to effectively damage him. It's not a super drastic change in appearance or pattern. But it still counts. You thought you had it won but surprise here's phase 2.
Jacquio though, has 3 phases and all 3 are drastically different phases with wildly different appearances, environments and objectives. It's a much more creative multi-phase boss fight. However Ninja Gaiden came out a year later, and I'm betting by 1988 there were more of these multi-phase boss fights and I just can't recall them all.
But the earliest I can actually think of is Dracula from Castlevania who after you kill his first form, turns into a big white gargoyle hopping around the screen, affectionately referred to by fans as the Cookie Monster. There's a bit of luck in guessing right when he is going to do a big jump and a small jump when it is time to get under him to the other side. The rest is knowing what he's weak to and how to attack. The first phase is a little more skill in timing the whip against his fireballs and then getting an attack on him before he disappears. It's a solid 2-phase fight that includes 2 very different skill sets and very fitting end to a great game.
So what are the earliest 2-phase boss fights you can think of?