Its not guaranteed, but it will happen enough that Gideon will be played, use first ability, setting up an ultimate ability on the next turn
On the downside, it costs double white, which makes it a lot more difficult to cast in multicolor decks on turns 2 and 3
As someone who is striving to complete such missions and hasnt been lucky enough to complete more than one of them just yet, the below list of Secret Mission conditions is provided by the folk over at Pokemon Zone
We can see a variation of this card where it probably required player damage to trigger the ability, and came with a sneak cost
However, that power comes at a risk
[2] If you dont want to worry about building your own deck right away, purchase a starter deck that has all the cards you need to get started