I know I should know this, but I forgot what is the deal.

Can I play He Calls It Thinking: Response: Cancel the effects of a response without an influence cost. Then, attach He Calls It Thinking to a HM character (counts as a Boon attachment with the text "Attached character gets +2 STR."). Even without having a HM character I can attach it later?

And can I play Ill Tidings: Challenges: Kneel a Maester or a L character to choose and discard 1 attachment from play. Then, if you have no power on your House, draw 1 card. Even when there is no attachment to discard, but I just want to draw the card

Rozy said:

You could play He calls it thinking, but no iii tiding.

The deal is that He Calls It Thinking has no target (no word "choose"). If you succesfully cancel some response, then it attaches to HM character (even if the only HM character is controlled by opponent) or it's simply discarded.

Ill Tidings has a taget, so you cannot play it if there is no attachment on table. Moreover, even if it had no target, you still couldn't draw, because of unsuccessful attachment discarding.

Rogue30 said:

Both of the effects you are asking about are in the "Do X to do Y, then Z" format. (Granted, He Calls it Thinking doesn't have an X, but you get the point.)

Now, it is true that when you are going to play an event, all specified targets (as shown by the word "choose" must be present and you must be able to pay the cost. However, when you are dealing with a "then" effect, you only have to satisfy the play restrictions and target requirements on the "Y" part before playing the event, not the "Z" part (after the "then"). This is because "Z" is dependent on the successful resolution of Y to begin with.

If you apply that general rule to the cards in question, you get the results Rogue outlined.