Mark Zuckerberg posted his first tweet in more than a decade, a playful jab at Elon Musk on the day the Meta Platforms Inc. founder rolled out a much-anticipated Twitter substitute.

Meta’s Instagram officially unveiled Threads Wednesday, considered the most potent threat yet to the struggling social media service Musk owns. Hours later, Zuckerberg tweeted a photo of identical Spider-Men facing off.

Zuckerberg’s tweet was his first since 2012 and comes days after Musk challenged the Meta founder to a cage fight.

Threads is capitalizing on a series of mis-steps at Twitter. Since Musk acquired the company for $44 billion in October, it’s cut thousands of employees, loosened content moderation policies and put users and advertisers through a spate of technical challenges. In the latest controversial policy change, Twitter limited the number of tweets users can view daily — a measure Musk called “temporary” in order to fend off data scrapers and bots.

“There should be a public conversations app with 1 billion-plus people on it,” Zuckerberg said Wednesday in a post on Threads. “Twitter has had the opportunity to do this but hasn’t nailed it. Hopefully we will.”