Skip 4 Achievement in Vampire Survivors

Each of the Skip achievements is for surviving until the "end" of a bonus stage. Refer to Boss Rash (5G) for unlocking all of the bonus stages.

The first three bonus stages (Molise, Moongolow, and Green Acres) don't have anything special about them that impacts how you play them in any way. The fourth (Bone Zone) and fifth (Boss Rush) are a bit different, and are covered in their own achievement solutions.

Since these aren't really much different from normal levels, all the same strategies apply for surviving until the end of the bonus stage: get your three best evolved weapons (Santa Water, King Bible, and Axes), as well as the evolved Lightning Ring, Spinach, and whatever your starting weapon is, and you shouldn't have any issues surviving until the end of each of the first three bonus stages.

Note: The Yellow Sign relic is obtained in Moongolow by reaching the end of the stage while playing as a normal character. It's therefore most efficient to do your 15-minute run of Moongolow while playing as a non-secret character. My recommendation is Pugnala, as she's fast, strong, and has good starting weapons.