Everything can be counterfeited.
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.
There should be, but that can be counterfeited too.
Capable of being falsified, counterfeited, or corrupted.
Need more info since they aren't counterfeited.
Not really, except for the melt value of whatever metals they contain.
40-60 dollars depending on condition.....Beware....Highly Counterfeited Card
Yes. The British issued counterfeit Continental money during the Revolutionary War.
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.
Coins are struck, not forged, unless by "forged" you mean "counterfeited". There's more information at the Related Question.