Because the Late Game (more than 1Million HC) is getting longer and longer, here is some Achievements ideas that could help with that.
Name : Devil Switch
Goal : Buy the Golden Switch at its highest Cost (in other words, buy it while you have a x666 bonus)
Quote : "Can you feel the waste ?"
Name : Satan is Santa
Goal : Get a Reindeer within a x666 Bonus
Quote : "This is an odd combination"
Name : The Completion
Goal : Buy all Seasons Upgrades (eggs, halloween, valentine, christmas)
Quote : "Now it's done"
Name : Reach the 0
Goal : Have exactly 4'321 Buildings and sell them all
Quote : "Will you ever be able to raise again ?"
Name : Lucky Luck
Goal : Miss a cookie during a Cookie Chain and start a new Cookie Chain
Quote : "This cookie gone faster than its shadow, but still"
(Reference to Lucky Luke)
Name : The Prism Game
Goal : Get 1 prism with just Cursors and Grandma (Player never bought farms or over)
Quote : "Reach the top of the ladder with only first rungs"
Name : Perfect Grandmas
Goal : Buy 300 Grandmas and ascend without the Bingo Center/Research Facility bought
Quote : "We avoided the Requiem, it was a peaceful game session"
(Reference to Requiem for a dream, I think it's a good one since we are talking about addictions and grandma haha)
Name : Hand-Made > Industrial
Goal : Get more Hand-Made Cookies than the number of Cookies forfeited before Ascending
Quote : "Real people prefer it tasty"
Name : Clicking Power
Goal : Click the cookie after buying every upgrades that gives more clicking power (Prestige Upgrades Included)
Quote : "How many did you get ?"
For more Achievements Ideas, I think we could mind about Prestige upgrades and Auras.
Let me know which ones did you like :D