、！
Alright — bring it on!
Literal
Alright, attack-[て]-come-[imperative-こい]!
Combat-challenge expression. かかってこい is the imperative of かかってくる ('to come at, attack'), formed from the て-form of かかる plus the rough imperative of 来る (こい). The ~てくる compound-verb construction expresses motion toward the speaker — literally 'come at (me) attacking!' — and functions as a standard 'bring it on!' challenge.