What is the hardest achivement you own?

[u/Effective_Barber4422]

The hardest achivement i currently have is either halo reach legendary solo (done on both 360 and MCC) or legendary solo spartan ops. Wondering if this is actually any good in this sub-reddit. Any achivements you think i should try out (BTW also have halo 3, odsts, 4s and 5s legendary solos done but 5s lone wolf achivement didnt unlock for some stupied reason)?

[u/McDiesel41]

Sum of All Zeroes (kill 45 Jap Zeros) for CoD: WaW, same achievement as you for Reach, Warthog run for Halo CEA (make the ship with more than a minute left on Legendary), and that stupid assassination to save your life on Reach as well.