When testing out a game concept, it's natural to receive negative reactions. Getting these out in the open so you can weed them out is kind of the point.In the case of Halfbrick's Tank Turn Tactics, however, playing the game across the office managed to damage friendships, instilled a sense of paranoia and mistrust, and even turned those who weren't playing into double agents.It's an experience, CCO Luke Muscat revealed during his talk at GDC in San Francisco, that illustrated the power a game designer has.It also served up a promising title that, to this day, sits on the shelves at Halfbrick waiting to be revived.The goal, Muscat explained, was to make a massively multiplayer game, simple enough for everyone at Halfbrick's office to play at the same time.Initially delivered in physical form  a board hashed out in a room in the centre of the office  Tank Turn Tactics was a game designed to take place across a grid. Every player takes charge of a tank, and is assigned a set number of 'action points'.These points  refueled every day with one new point  allow players to move across the grid and fire at any opponents in the direct vicinity.The interesting element about the game, however, is the ability to gift action points to others in adjacent squares."I thought it would create a bit of excitement," Muscat said."Anyone who approached you, they may shoot you, they may help you. You just don't know."Play didn't turn out as Muscat expected, however.Instead of shooting each other, players teamed up and passed their action points from person to person so one player would have enough points to take out one player on the other side of the grid.In one case, their target was their boss.Later games then saw players pairing up to exchange points before turning on each other, and  in extreme cases  led to people spending hours of their day devising strategies for victory.Even those not playing the games served as spies, listening in to the conversations of rivals and feeding the information back.It sounds amusing  and, indeed, Muscat's talk was peppered with laughs  but he also revealed that a few of those working with Halfbrick came to him to complain."There was some genuine animosity brewing between people in this game," said Muscat."A player came to me and they were upset  really, really upset. It was damaging his relationships at work, making him not want to come in. That's not what we wanted to happen at all. And so, the game was canned."Muscat said a survey revealed that more than half of those who had played the game had "felt upset" at some point, even though they'd become dedicated fans and played it religiously.This wasn't the reaction he'd been looking for."I was in two minds," concluded Muscat."Actually, I was in three minds. Part of me thought 'this will make a great GDC talk one day'. I also thought I'd made something compelling. But, on the other side, the game had damaged the office."People no longer trusted each other, he said, and others were genuinely hurt when their friends conspired to take their tank out. It stopped being funny.Muscat hasn't given up on Tank Turn Tactics entirely. It still exists, and he plans to fiddle around with it in an effort to eliminate some of the problems Halfbrick encountered.However, the whole experience highlights the power and responsibility a game designer holds, and the fact that engagement doesn't always mean success. If a game starts to destroy previously solid relationships, then chances are, it's not the finished article.You can read more about Tank Turn Tactics in our extensive follow up interview with Halfbrick's Luke Muscat here