This card really stands out as a clearly powerful monster that will have a role in defining the texture of standard for the entirety of its tenure in the format. Many Red mages were worried that with the exit of Thunderbreak Regent, Red aggro would no longer have a solid top-end finisher that is difficult to interact with. It’s beautiful how Skyship Stalker fills that role while having perfectly opposite strengths and weaknesses.
First of all, the stakes are higher than Thunderbreak–the floor is lower but the ceiling is much, much higher. Although it is a squishier turn 4 play than Regent, in this case your opponent had BETTER have a removal spell ready because if you untap with this in play on turn 5 they are not long for this world.
Whereas Thunderbreak Regent punished the opponent for trying to interact with it through targeted spells and abilities, that is precisely what is needed to deal with Stalker cleanly. Conversely, the best way to handle a Regent was by having a creature that was bigger, while Stalker, with its evasion and first strike/firebreathing combination, makes trumping it with a creature well-nigh impossible.
But one of the reasons that I’m so high on this card is that it mitigates its own weakness by granting itself haste. An experienced player will patiently wait for the right moment to deploy this threat when the opponent is either out of removal (a common occurrence when facing Red aggro decks) or tapped out to punish the opponent by sinking all your mana into it. Moreover, having this in your list makes the top of your deck scarier and scarier the longer the game goes.
Even though having multiples grants diminishing returns (as is the case with any firebreather) I think this card will be enough of a lightning rod for removal that having 3-4 will be fine for many decks, although a truly hyper-aggro deck may want only 1-2 or none if their curve and land count is low enough that they can’t support it. We’ll see what happens, but one thing is for sure: Mountains just became much more dangerous.