Double-checking the rules for the Spy here... I imagine others might find the answer helpful as well...
The rules state:
To activate a diver belonging to an opponent (directly on your left or right), spend 1 Credit and use the effect of the diver located on the same level as your Spy on your opponent’s player board. Resolve the effect of that diver as if it were on your player board. Therefore, you cannot copy your opponent’s Spy to activate a diver belonging to an opponent who is not directly on your left or right.
My main question is:
1) If I copied another player's Explorer using a Spy that was not upgraded, I would need to pay one credit for my Spy activation (payable to the other player, if using the "advanced" variant). Then I would need to play 2 credits to the bank to utilize the Explorer ability. Correct?
A few more small questions...
2) If my Spy is upgraded, there is no Spy activation cost, so the other player receives no credit as compensation, even if I spend credits to activate their token's power. Correct?
3) Can I use a Spy, upgraded or not, simply to send another player's token to the top of their stack, should I choose not to activate the diver ability?