PewDiePie is currently in a major battle with another youtube-channel, T-Series.
For over 5 years, Pewdiepie was the biggest youtuber on the platform, but now a new contestor has showed up. PewDiePie is trying to stay the biggest, but T-Series is growing faster than PewDiePie and could potentially take over PewDiePie's number one spot.
PewDiePie, desperate to stay the biggest, teamed up with other youtubers, MrBeast (who has more than 10 million subscribers) and Markiplier (who has more than 20 million subscribers). Together they are trying to keep PewDiePie the biggest.