well it's not game mechanics, it's more like the plot. like just the basic setup "X is at Y go beat them." i want to include tho because it's a metroidvania-ish thing. i could just dump them right in with no explanation, and just make the start very linear but i feel like it's p unengaging. on the other end i could do long cutscene but i actually usually hate games with those.
i feel like showing and telling with plot is super hard compared to gameplay tbh. like i could just open up with a long cutscene and stuff but tbh i feel like most games i play with that kind of thing are really boring / wanna skip all the text. but then doing it interactively requires a ton of setup. like DOOM does it really well i feel like. the opening gives a good sense of atmosphere + while not being boring. or like link to the past i think does a good job of making the opening non-action parts really concise.