The offseason and preseason work over, the Cardinals officially had their first regular season practice Monday, yet there is still a mystery surrounding the offense that coach Kliff Kingsbury will unveil Sunday against the Detroit Lions.

Whether that will be an advantage, Kingsbury acknowledged Monday, "I don't know."

"You can go back and see stuff I did the last 10 years in college, not that this is what that'll look like or not," Kingsbury said. "But it's not like this is my first year of calling plays in football."

That doesn't mean the Cards are going to stop playing coy – "You'll have to see Sunday," running back David Johnson said when asked about what the offense will look like – or tamp down the excitement the players have to finally get to run it.

"I think Kliff and the guys have done a great job keeping it under wraps," running back Chase Edmonds said. "We've kept it really vanilla, super vanilla and super basic in preseason. After seeing some of the install plays we have, it's very creative. I can't wait for the opening up … it's kind of like Christmas, or Christmas Eve-type of deal."

Some of the Cardinals' coaches have been working on Lions' prep fully since the third preseason game in Minnesota ended. Kingsbury said the initial Lions' study began in the summer, but as the Lions don't know exactly what Kingsbury will do on offense, the Cardinals can't be certain how Lions coach Matt Patricia will tweak his defense from his rookie head coaching season.

The Cardinals only kept two tight ends on the roster and seven wide receivers, but Kingsbury said Monday the Cards could use a reserve offensive lineman as a tight end in certain situations.

Rookie quarterback Kyler Murray has looked mostly solid in his preseason games and practices, save for a rough outing against the Raiders. He has found a nice chemistry with fellow rookie KeeSean Johnson, but the Cardinals also figure to lean on the usual suspects – running back David Johnson and wide receivers Larry Fitzgerald and Christian Kirk.

"Preseason was rough because we couldn't do much," David Johnson said. "He's already started doing a little bit and it looks really good for our offense and as a whole, with what he is doing with his creativity."

The concepts have long been part of practice, although Kirk said the players don't dive into specific opponents – the Lions this time around – until the week of the game.

Kingsbury had the Cardinals go through a "regular" game week leading up to the Vikings' preseason game, including practice schedules. That's where the Cards are now, spending Labor Day laboring and then the players getting Tuesday off as the coaches finalize the game plan leading into the bulk of the practice week.

"It'll be a fun show," tackle D.J. Humphries said. "I think we're going to shock a lot of people."