Meaning:
Lit. “only once” – which in standard Polish would be “tylko raz” but the expression actually comes from southern Polish dialects, especially gwara podhalańska.
It is an uncommon case of a local dialect phrase being adopted to a nationwide vocabulary. It got popularised especially by the 70s TV series about the famous mountain brigand Janosik. A kind of Slovak/Polish Robin Hood.
The meaning can be translated as something final. And especially: a one blow that will knock you out or kill you. Used either as a threat or means of admiration to someone’s martial prowess.
Examples:
Niedźwiedzie Młocisko. Takim jak trachniesz, to ino roz. Gdy twój bohater zaatakuje, dobierz kartę.
Nie wkurwiaj mnie. Bo jak ci przypierdolę ze skilla, to ino roz.
Hem — kiwie Wojtek głową — moiście wy! Ma mi baba za usami mrajceć, majom mi dziecyska koło ścian brzejsceć, je! Bajto! Śmierzć to ino roz, a horość to ta tys nie przez umiar.