I had a crazy game that involved Claw and Industrialist.
The Claw is an alien that allows you to choose a non negotiate encounter card from your starting hand and place it aside face down. Once per encounter, if a player plays that same card as your face down card, reveal your card. At the end of that encounter, choose a planet from the player's home system and add it to your own. Any ships on that planet go to the warp and the planet is considered a foreign colony.
As a main player, after you lose an encounter in which you have revealed an attack card, your opponent must either allow you to win the encounter instead of losing, or else allow you to place your attack card faceup on this sheet, adding it to your "stack". Your stack is not part of your hand and cannot be drawn from by other players or affected by other powers.
As a main player, after you reveal an attack card, use this power to either add or subtract the total of all the faceup attack cards in your stack from your side's total. For instance, if you have an attack 08 and an attack 12 on this sheet, you would add or subtract 20 from your side's total.
Early in the game, the Industrialist added an Attack 08 to his stack. From that point on, the Claw used an Attack 08 card as his claw. Every time the Industrialist was involved in an enounter and played an attack card, his stack was also added to his attack number.
We spent many minutes debating the wording on the Claw's power for "if a player plays that same card". Is using a card from the Industrialists's stack counted as a "play"? It seemed pretty outrageous because the Industralist's power is mandatory, so he would either have to negotiate on his turn or give one of his planets to Claw.
Normally I would consider a "play" to be using a card in such a way that generally uses it up and takes it out of the game, or the player has to choose to use it. If there's a card that gains an ongoing effect and is mandatory, I'm not sure if that's a "play". In that same game, Citadel was also one of the players and we determined that they would only "play" one of the citadel cards if the citadel was activated (not when adding a card to a citadel).
In the end, we decided to let Claw have his fun. We were all so drunk and it was getting late.