Even though this is for fun, I will critique anyways.
Barbarians -- It is Bazaar with an additional attack, so why does it cost less? Even though the attack hits you as well, it is symmetrical so it has to cost at least as much as Bazaar. Plus, since you are the one inflicting the global attack, you are probably better able to deal with it.
Infanty, Plaque -- I don't like the idea of attacking only one person, even though you don't get to choose who. That's personal preference though. For Infantry, is the attack on gain as well? It seems that way from the phrasing, but then the card has no actual function aside from on-gain effects.
Black Knight -- This is a Laboratory with an additional Embargo power. The additional ability means it should cost more than Lab!
Revolutionary -- This is too strong for $4. Not only is it a duration (potentially "ruining" opponents twice per reshuffle!), it's also a cantrip?! The on-gain penalty doesn't really stop it at all. There are very few non-terminal attacks. There's Familiar, which is difficult to obtain due to the potion cost, and there are Minion and Urchin, both of which do not stack. Revolutionary is just too strong to be a cantrip and a duration and still cost only $4. Man.
Now back to your fun ideas.