Everything can be counterfeited.
Pass counterfeited
Yes. The British issued counterfeit Continental money during the Revolutionary War.
Yes.
First of all, paperclips are too common to use as money. Second, they can be made to easily, or, if we talk like they are money, "counterfeited". So, people would not have to earn them, they could just make them.
Unfortunately, no. You can pretend to steal money, but you cant actually take other peoples money. If you cant drop the money or transfer it, it cant be done. Sorry.
A very good question. All key-date collectible coins have been counterfeited for many years, that's the simple answer. As to the most, all one & three dollar gold coins struck by the US have been counterfeited and all Trade Dollars also.
Large weights to carry large values. Difficult to trade quickly ( liquidity ). Difficult to hide from robbers. More easily counterfeited or copied.
There should be, but that can be counterfeited too.
Capable of being falsified, counterfeited, or corrupted.
$20
The artistic designs used on some currency were considered too easily counterfeited since the counterfeiter could make numerous errors and because of the complex design those errors would be difficult to notice. A simpler design, while easily counterfeited as well, does not conceal the errors as well as the older complex designs.