When do you discard? Immediately after drawing, and before playing more actions? Or can you start/continue a chain of actions, which might include drawing more cards, and then discard after? I understand that all unused cards get discarded, so doing so at the end of the turn would negate Oasis's penalty, but the card is curiously vague about when this discard occurs.

Oasis:

• I'm guessing that by "before starting your action phase" you meant "before playing another action card." Note that "+1 Action" means "add one to the number of remaining actions you have for the turn". It does NOT mean "play another action." – GendoIkari Nov 5 '14 at 19:38
• @GendoIkari Yes, sorry, that's what I meant. Will edit – user30903 Nov 5 '14 at 19:43

You do everything on the card in the order it says:

• Draw one card.
• Add one to the number of remaining actions you have for the turn.
• Add one coin to the amount you have to spend this turn.

And then you can move on to other Actions or your Buy phase. So you'll discard a card before you play any other actions. (But it's during your Action phase, of course - it has to be since you played Oasis!)

• Do note that cards may have effects that don't happen when you play the card, but rather when you do something else (i.e. a Reaction's reveal effect, a card's on-gain effect, or a card's on-trash effect). – Powerlord Dec 4 '14 at 19:47

You start your turn with a "bank" of 1 Action, 1 Buy and 0 Coins. During your Action phase, you may spend 1 Action to play one Action card from your hand. If you do, then you do everything that the card says on it, in order, to the best of your ability.

If the card says "+(n) Card(s)", then you immediately draw that many cards from your draw pile. If you need to draw a card, and your draw pile is empty, then you shuffle your discards to form a new draw pile and continue drawing. If your discards are also empty, then you don't get to draw any more cards.

Anything else the card says, you apply that effect immediately. In the case of Oasis, that means that after drawing a card and adding one to each of your Action and Coin banks, you discard a card (if you have any cards left in hand). You may then play another Action card from your hand, if you have one.

This becomes very important when you're resolving cards via something like Throne Room. For example:

• Spend an Action to play a Throne Room
• Select Oasis to play twice
• (First play of Oasis) Draw a card