See Bullet-Eater concept #1. Now get bullet-eater during your turn.

If the creature died this turn, you don't control it any longer.

--> "for each creature that died under your control this turn"

There is tension in the card design where the effect of the ETB actually is very restricted in the time-window it is useful to you (before blockers are declared, easily first main phase - which makes flash less relevant), but the most common death opportunity is during combat after blockers are declared.

A tap-freeze-effect would be more natural for this design since - though better used before combat - it would still be useful used EOT.

Blue does have enough effects that could be used second main phase or during an opponent's turn that you shouldn't need to resort to this.

You can check morbid cards to see what options black, red and green use for similar design space (removal, token creation, card draw/tutoring ...) and addendum for effects that make sense at instant and sorcery speed (since scaling morbid often means second main phase-ish).

Blue does have several 2+ power at or less (even for free Demilich). They can also get 5/6 for or less (possibly better value than other colors).

Bullet doesn't sound Magicky.

As already pointed out, none of these abilities synergize.