Eventually, planetary nebula keeps expanding outward and becomes part of the interstellar medium. Left with the bare hot core which is a white dwarf. No source of internal energy so it just cools off. Ending of the Sun. Shorter main sequence life-times, shorter lives afterwards as well.
More mass compresses hydrogen burning core more so that rate of nuclear fusion is higher.
They make the rate of the hydrogen fusion go even faster. No helium flash, start of helium fusion happens slowly. When this happens, carbon fusion can begin . Burning goes faster for each successive element. Get shells of burning, too, with a layer of hydrogen burning, layer of helium, etc.