Assassin's Creed: Revelations - Den Defence
One of the new additions to the Assassin's Creed series for Revelations is the Den Defence mini game. It's a simple tower defence game wherein enemies attack in waves down a narrow channel and you set up obstacles to keep them back. To put it bluntly - it's not very good, but it's not something that needs to be constantly done. However if you manage to win 3 such games that ticks off one of the items for the Assassin's Guild challenges which leads to a nice upgrade. So what's the problem?
The problem is that if you're playing the game 'properly' you never have to play Den Defence beyond the introduction. The mini-game initiates when the enemy becomes too aware of your presence; their awareness can be lowered by various easy means so there's little excuse for allowing it to escalate. If by some miscalculation it does jump to the point they attack if you've been training up your little assassin band you can appoint one of them as the Den leader and they will play the mini-game for you.
So the only way to gain this upgrade is to screw things up, which rankles.