Do actions that affect all cards also affect cards in your hand.?
Playing Howl, will not allow First Mate to be played on the Tsar's Palace base.

In this thread on BGG, Mark Wootton, who appears to be AEG's Director of Company Development said:


  Q: What about the Homeworld base ability and the War Raptor? The Homeworld states that when you play a minion on it you can play another minion of Power 2 or less. Is the Raptor a valid play, since before it's added to a base it's Power 2?
  
  A: The order of effects is:
  
  1) To play an extra minion check its power is correct. War Raptor = 2 Power
  
  2) Any abilities on that minion trigger. War Raptor becomes 3 (or more) Power 
  
  3) Trigger any ongoing effects in play e.g Leprechaun or Flame Trap
  
  So if, for example you had an action played on the base that said "All your minions here gain +2 Power" you could still play a 2 power minion there. Because it is 2 power when it is played.


The base checks first if First Mate is the correct power, before Howl is applied.

(Note: I disagree with Mark Wootton's last example, although it is immaterial to the correct answer here. I contend that an Action worded as he suggests would only affect Minions currently "here" at the base. For the Action to affect Minions played later that turn, it would have to be an Ongoing effect (that might be what he meant, as there are Actions that are played on a base with similar effects).