Allies in battles appear only on certain days. They attack Clockworks that come within range, but they don't attack Bosses. Allies may go through gates, however their AI does not always pathfind correctly, so they often get stuck behind walls, away from the action.
There are two types of allies in battles: Kingdom Force and Archineers. Kingdom Force have limited health, and once defeated by Clockworks, do not reappear the next day. The Kingdom Force units that can aid Lock in Battle are the Archer, Knight, Pikeman, and Veteran. Archineer allies have unlimited health but appear much more rarely. The two archineer allies are Isaiah and Heathern.