You can use pacifist with the meaningless handicaps -attack% and no bombs, and with cheats: -bullet speed, 2 extra hearts, drop hearts and more items (last 2 work with bosses) and STILL GET A STAR. This is easier than normal because slower bullets, less bullets because none from dying enemies/barriers, more lives and even replenish with bosses when lucky, and STAR IS GUARANTEED. enjoy!
For those who asked for harder puzzles, there's lots of them on griddlers.net. Unlike the dev of this game its a completely free site. You can find there this type if puzzles (under Number Logic Puzzles) as well as others types you might have seen before. You can also find there very attentive staff and live community. Give it a try, you won't regret.
 "Bullet Heaven 2"){kind=icon}
 "CalcuDoku Light Vol 1"){kind=icon}
 "Meganoid"){kind=icon}