Hayley Atwell and Clark Gregg have spent the last few months entrenched in a bitter rivalry of Dubsmash videos. The "Agent Carter" and "Agents of S.H.I.E.L.D." stars will up the stakes when they go head to head on Spike TV's hit show, "Lip Sync Battle."

The second season of the faux-singing competition series will feature the Marvel TV stars, who recently shot their episode set to air in 2016, according to Entertainment Weekly. Without giving away their song choices, Atwell and Clark both tweeted after their performances.

Competing on "Lip Sync Battle" caused a slight delay in the actors ongoing Dubsmash Wars for Charity, which will enter its third and final round on Wednesday. Atwell's #TeamCarter and Gregg's #TeamSHIELD will both drop new Dubsmash videos and the winner will be announced on Oct. 16.

"Something happened. An opportunity presented itself to settle a very personal score once and for all to the death," Gregg announced from the set of "LSB."

The competition between the casts of the ABC show will benefit the charities Stomp Out Bullying and St. Jude Children's Research Hospital. Fans can vote for either #TeamCarter or #TeamSHIELD at CrowdRise by donating $1 dollar toward the video they like most. As of Oct. 5, #TeamSHIELD leads by about $5,000.

Click here to watch all the Dubsmash videos for Rounds 1 and 2.