Metal Slug Defense Mission 135 and Christmas Event

There might be a bug on this mission. It making it very difficult to defeat it. Been trying to beat it many times and no luck. Fix this problem please. As for the Christmas event, why does it cost so much to play a stage. Seriously. I have been playing this game for over a year and I have never seen anything as ridiculous as this.

Buckster87 about METAL SLUG DEFENSE