Most broken things in M+ history?

Hello all,

With the recent experiences people have had trying to clear Neltharion’s Lair (specifically Naraxxus) before the nerfs, I got curious about what other broken fights or trash packs Blizzard has released in Mythic+.

What are some of the most broken or overtuned (or undertuned) things, on release (before any nerfs), Blizzard has released into M+ dungeons? I started doing M+ at the start of Shadowlands and I can’t really remember anything that’s as bad as pre-nerf Naraxxus this season.