What was in the 6th coffin in Naruto

In Naruto, when Kabuto conjured the sixth Coffin to terrify Obito and demonstrate his might, it included Madara Uchiha. When it came to knowledge about a wide range of topics, Kabuto was an expert.

Why was Tobi terrified on seeing the 6th coffin? I know it was

COMO KABUTO ENCONTROU O CORPO DO MADARA PRO EDO TENSEI #naruto

Who was in the 6th Coffin REALLY?

What was in the 6th coffin which Kabuto summoned in front of Tobi

Madara Uchiha, Naruto-Fanon Central Wiki

kabuto 6th coffin｜Pesquisa do TikTok

Six Paths Sage Mode, Narutopedia

Spoiler] What was inside the coffin Kabuto showed Tobi : r/Naruto

What was in the 6th coffin which Kabuto summoned in front of Tobi