With the recent discussion on Guardian - what if you can optionally trash it at the start of your turn to get a second +$1?
Transferring Coins 2:2 from turn to turn is probably too good. ...
Not just that, you'd get the Attack protection to boot. I think that's far too strong, no $2 card should be an automatic buy with $2 and a buy left. (Even a strong cantrip like Hamlet isn't always.) It'd also outshine Embargo for getting you the +$2 one shuffle earlier...
Even allowing optional trashing for no extra benefit would substantially boost Guardian, removing a delayed Copper from your deck for free. It would still be an automatic buy this way, converting $2 now to $1 next turn is better than just wasting it. Unlike Tax, it can never hurt yourself (unless you want to be attacked).