The phrase "killer combo" refers to a combination of things or factors that work together exceptionally well or have a powerful impact. Full definition
Rather, this die - off may have been the result of a more subtle killer combo: too little moisture accompanied by too much heat. (ensia.com)
Berries and nut butters make for such killer combos, so you've got free reign here. (gnom-gnom.com)
From developers Picomy, who were responsible for Heroki [$ 4.99] and played a part in the upcoming Sonic Mania console release, Monomals is touted as a music game with some eccentric fishing elements, which sounds like a definitively killer combo. (toucharcade.com)