The rules for Red Force secondary actions in the core Horizon Wars: Zero Dark rulebook were kept intentionally simple and, for Versus missions, are really all you need.
For Solo and Team play, though, it can sometimes make it a bit too easy to just constantly cautious move your way across the table, dodging the Red Force and never getting into a fight. Now, if you can make that work, more strength to you and it can still be an interesting intellectual challenge. But if you'd like your Red Force to be more unpredictable and dangerous, replace your secondary action with the following rules:
Roll a d12.
On a result of 1-6, the bogey moves this many inches towards the nearest character.
On a result of 7-12, the bogey will shoot the nearest character in LOS and within this range. If there is no character in range and in LOS, the bogey makes a normal move instead.
On a result of 12, once the bogey has resolved its secondary action, the bogey closest to the one that just acted performs a secondary action as well. Roll again.