Not speedrun related, but to give Jack Bros., a game with relatively one-and-done levels, some replay value, here is a high score challenge.

There are eight categories: Two difficulties each for all four characters.

Select "Start" and complete the game with no continues. Whatever time is remaining at the end of the final boss, that's your high score.

There's also a less important IL variant: either Start (first level) or enter a Password (other levels). Reaching a level after doing another one and having an advantage is not allowed in ILs. 48 categories for this naturally.