x2
-20Sand AttackIf the Defending Pokémon tries to attack during your opponent's next turn, your opponent flips a coin. If tails, that attack does nothing.
EarthquakeDoes 10 damage to each of your Benched Pokémon. (Don't apply Weakness and Resistance for Benched Pokémon.)
When I try to attack, does Marowak's "Bodyguard" Ability prevent me from having to flip a coin if my active Pokemon was attacked last turn with Silicobra's "Sand Attack"?
The effect of Sand Attack is on your Pokemon that was attacked, not on you. So, Bodyguard does not prevent you from having to flip a coin to see if the attack goes through
If your opponent used Sandshrew's "Sand Attack" on the previous turn, and you attack with Passimian's "Intentional Grounding" which requires you to discard a Tool from your hand or the attack does nothing, do you discard the Tool before you flip for the Sand Attack effect or after?
Flip for the Sand Attack effect first; if it's tails your attack ends immediately, or if it's heads you proceed with your attack as normal.
If I have a Tera Pokemon on my Bench when I use Landorus' "Earthquake" attack, do they take 10 damage or not?
No, the Tera Trait protects them from damage by your own attacks as well.