Seismic Shift (Red)

As an additional cost to play this,

X Seismic Surge tokens you control.

Destroy X target aura tokens.

Go again

Rulings

From the Compendium of Rathe release notes

The additional cost value of tapping X Seismic Surge tokens is determined at the time the card is declared to be played. This is so that X targets can be declared for Seismic Shift’s second ability.
You must have a target to play Seismic Shift for any X>0 when paying its additional cost. E.g. You cannot play Seismic Shift tap 4 Seismic Surge tokens for its additional cost, if there are not at least 4 aura token targets.
You cannot target non-token auras with Seismic Shift.
As Seismic Surge tokens have the aura sub-type, you can tap to pay for the additional cost and also target them as well.
You can still play Seismic Shift if you declare X=0. Doing so means that you will not tap any Seismic Surge tokens you control when paying the additional cost. Additionally, when Seismic Shift resolves, you will not destroy any aura tokens. You will gain an action point from resolving go again.
If all targeted aura tokens are destroyed before Seismic Shift resolves, you will still gain an action point from go again.

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)