For example, lets say its the fourth round and my opponent has a 2 drop spoiler in play. Its my init and i plan to drop Terra. In response to my recruiment, my opponent evades Spoiler before Terra comes down on the board. So as I recruit my Terra, my opponent's board consists of a stunned Spoiler. I have an Argus in play and I wanna blow it up. Can I target the stunned Spoiler and subsequently replace the Argus I have in play? Terra's text doesnt say stun a NON-STUNNED character, but simply stun a character. Is this possible?

Another example, Blackgate Prison. Blackgate prison doesnt say stun a non-stunned character, but just a stun a character. So during the end of my combat... can I use Blackgate Prison to stun an already stunned character so I can draw a card?

Can I get a judge's ruling? Thanks guys.

HB

you might want to use the search engine next time :p
Terra: Like you said it doesn't say non-stunned character. so yes a stunned character is still a legal target. when the effect resolves it will do as much as possible (in this case replace a location). Since you can't stun an already stunned character he won't take any damage.
Blackgate Prison: Notice that stunning here is payment for the action. And you must fullfil the payment costs before the effect can go to the chain.
Otherwise terra could stun characters while she is exhausted lol

Terra doesn't require that you attempt to stun an unstunned character. The only requirement for her effect is that the target is a character with a cost of 3 or less. Terra will attempt to stun said character, but it is already stunned, so it won't do too much to it. You can get rid of your Argus this way.

Blackgate Prison is different, however. Unlike Terra, where the stun is part of the effect, Blackgate Prison has stunning as a cost to use the effect. You are required to actually stun a character to fulfill the cost. If you can't do this, you can't use the effect of Blackgate Prison.

Thanks for the clarification!