The spot price on unregulated exchanges which are presumably operating fractional reserves, wash trading, front running, and spoofing the order book.
And don't forget 3 billion Tethers, likely being used to manipulate margin trades. (see "the bart" pattern, which is likely an indication of either Bitmex or Bitfinex wiping out margin traders with temporary price manipulation)
https://papers.ssrn.com/sol3/papers.cfm?abstract_id=3195066
https://amycastor.com/2019/01/17/the-curious-case-of-tether-...
https://omniexplorer.info/address/1NTMakcgVwQpMdGxRQnFKyb3G1...