I've seen some you could argue are a pump and dump, an actual Ponzi Scheme on a blockchain would be nearly impossible, it relies on a central ledger so the bad

I've seen some you could argue are a pump and dump, an actual Ponzi Scheme on a blockchain would be nearly impossible, it relies on a central ledger so the bad actor can disproportionately transfer the new investors' assets to old. There's been a recent example of someone running a Ponzi using BTC, but that's not an example of a currency being a Ponzi, which is a thing more specific than "scam."