Roman Reigns and AJ Styles are on a collision course once again, this time in an Extreme Rules Match.

It will be No Holds Barred when the reigning WWE World Heavyweight Champion defends his title against "The Phenomenal One" on May 22 at the Prudential Center in Newark, N.J. Reigns won their first encounter last Sunday at Payback and there was plenty of interference throughout that clash.

With no disqualifications and no countouts for the Extreme Rules match, there will likely be even more interference this time around. Here are five possible candidates to get involved in the main event come May 22. To view this article in slideshow form, CLICK START at the top right of this page.

1) Karl Anderson & Luke Gallows

This seems virtually guaranteed since Styles' former NJPW buddies have been getting involved in his bouts left and right -- including the last main event at Payback. There could potentially be a swerve where they come in and help Reigns, forming a different kind of Bullet Club and getting the Leader of the Roman Empire instantly over if the WWE was bold enough to turn him heel amid the boos.

2) The Usos

If Anderson and Gallows stick to the obvious script of helping Styles, it's guaranteed The Usos will come out to respond on behalf of their cousin, much like they did at Payback. A possible swerve could see The Usos turn on Reigns, establishing themselves as the next threat to the tag division since The New Day has had a lengthy run with the gold and Enzo Amore's injury has created a void.

3) Finn Balor

The Irishman curiously was booked to drop his NXT Championship to Samoa Joe at a non-televised event last month in a move that could signal his impending arrival to the main roster. Though he's booked to face Joe at NXT: Takeover in a rematch on June 8, several stars (Kevin Owens, Sasha Banks etc.) have appeared on the main roster at the same time as being a part of NXT. If Balor wants to make an immediate impact, he could get involved in the main event -- possibly forming the Balor Club with Anderson and Gallows.

4) Dean Ambrose

The "Lunatic Fringe" is "brothers" with Reigns, but he's been notably absent from the main event picture lately. Ambrose will likely face Chris Jericho again at Extreme Rules, but he could reinsert himself as a top player by getting involved in the main event. Ambrose could help his friend Reigns overcome the odds, or he could more interestingly turn heel by causing his former friend to drop the belt.

5) Seth Rollins

"The Architect" appears to be very close to returning, so he could very well make an impact come the end of May. Rollins has been sidelined with a serious knee injury since November, but he was healthy enough to film a movie starting in early April. If the filming is done, Rollins -- who never lost the WWE World Heavyweight Championship -- could return and instantly start a feud with Reigns, the current title-holder. Perhaps even better, he could return with Ambrose and reform The Shield with Reigns to combat Styles, Anderson and Gallows.

Who do you most want to see get involved in the main event of 'Extreme Rules?'

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