The Deus Ex: Human Revolution downloadable content includes a new boss fight - made entirely in-house by Eidos Montreal.

On Monday Deus Ex hit the headlines when it emerged that the boss battles were not developed by Eidos Montreal.

Instead they were outsourced to little known studio Grip Entertainment.

Deus Ex's boss battles drew criticism for their frustrating difficulty spikes. They also focused on action gameplay when much of the game encouraged the player to use stealth skills.

In a video posted online, below, Grip boss Paul Kruszewski admitted creating the boss battles was a tough job - and that he didn't know much about the Deus Ex world before the project began.

Next month Eidos Montreal will release The Missing Link, the first DLC for the game. The five hour add-on sees Adam Jensen stranded on a boat, stripped of his augmentations and weapons and interrogated by Belltower.

Towards the end of the DLC is a boss fight, which fans won't find as frustrating as those in the main game, Eidos Montreal told Eurogamer.

"We have a boss battle at the end, but it's different from the main game boss battles," Eidos Montreal production coordinator Marc-Andre Dufort said.

"You can actually not kill the boss. You can do a non lethal takedown on him. And you can kill him from afar. You can even kill him without him seeing you. It's more of a bigger challenge than a standard boss fight like we have in many games."

"Everything was done in Montreal at Eidos," he continued. "It's a lot less frustrating. But it depends on the way you play. If you played more combat in the main game, you probably didn't have any trouble dealing with the boss fights. So we allow the adaptation of the way you play for that particular boss fight."

Dufort said he understood why some gamers found the boss fights from the main game frustrating.

"I was playing more of mixed stealth and combat style, so I had some good weapons in my inventory," he explained. "I didn't have a lot of trouble dealing with. No, I didn't get any big frustrations dealing with them. But I can understand people playing more stealth style having some frustration dealing with those bosses."