Succumb to Temptation (Yellow)

If you've dealt arcane damage this turn, you may play this as though it were an instant.

The next time a Runeblade attack action card you control hits a hero this turn, look at their hand and choose a card. They discard it.

Go again

Rulings

From the Rosetta + 1st Strike release notes

The effect triggers the next time you hit. If the next attack action card you play does not hit, the effect may still trigger on a future attack later in the turn.
There is no priority between you choosing a card and the hero discarding it.
An action card played as though it were an instant does not cost an action point and can be played whenever the player has priority, otherwise it is still considered to be an action card.
If a card with go again is played as though it were an instant, you will gain an action point from the go again when the card resolves if it is your turn. Otherwise, you do not.

Keyword notes

Go again - Go again allows multiple actions to be played in a turn when usually playing an action with use up your action point, and therefore end your turn. A card with go again gives the controller of that card or activated ability 1 action point when it resolves.

When an action with go again resolves, its controller gains 1 action point.
Multiple instances of go again on the same card or activated ability do not stack. If a card or activated ability has multiple instances of go again when it resolves its controller gains 1 action point only.
If an action with go again does not resolve, its controller does not gain 1 action point.
You cannot reveal a card with no to Belittle. The card must have a value to its power that is 3 or less. (0 is a value)