My questions are: 1. If all my opponent’s characters have already been tapped, can I still attack with the newly formed Combiner? If all of your opponent’s characters have already been tapped and you finish an attack with your untapped Combiner, you will then attack a second time with the Combiner. When Bolster activates during my opponent’s turn, and Multi-Mission Gear is played with a Combiner Enigma, where does the attack land? As the defending character is no longer there, does it hit the Combiner?

The character they were attacking is part of your newly formed Combiner, so they are now attacking your Combiner.

If Thrust has a Grenade Launcher and boosts a character that is attacking, and the opponent reveals a Bolster, to play a Scrapper Gauntlets to scrap the Grenade Launcher, does Thrust donate 7 or 3 attack to the attacking character?

7 attack. The amount has already been locked in.

If I Bolster into a Multi Mission Gear, can I play Dampening Field and it activates?

You can play Dampening Field, but it would be past the point where it would trigger.

I have a tapped Flamewar - Veteran Decepticon with 3 life remaining with 2 other untapped characters and a facedown Bolster. My opponent has 3 untapped characters and taps their attacker, declaring Flamewar as my defender. Because the conditions are met, I reveal Bolster and play Multi-Mission Gear onto my Flamewar. That triggers Multi-Mission Gear and allows me to play an action, which I choose to play One Shall Stand, One Shall Fall targeting my Flamewar and one of my opponent's characters. This kills my Flamewar but the attacker still lives. What happens in this scenario? Does my opponent lose their attack because the defender was killed prior to battle cards being flipped? Or does my opponent get to choose another attack target?

Your opponent has already chosen who they are attacking, so the attack would end because there is no longer a defender.

I play a Bolster, and attack with my specialist. Turn ends. Opponent attacks my defender who is a specialist. I play bolster then I play Multi-Mission Gear, then for the action you play Peace Through Tyranny, KO’ing the specialist defender, effectively ending the attack with no flips. Do you get an extra turn, then a normal turn?

You take your extra turn, then your normal turn. You can’t take any additional turns.

When defending I reveal the secret action Bolster. I then proceed to play Multi-Mission Gear to play Brainstorm, in turn playing Battlefield Report and Defensive Formation. As these 2 have the same trigger condition as Bolster, am I able to reveal them now that Bolster has finished resolving?

In this scenario, it is too late to reveal them.

My opponent has attacked me, and I reveal the Secret Action Bolster. I use Bolster to attach a Multi-Mission Gear to a Specialist. I then use the Action granted by Multi-Mission Gear to play All-Out Attack. World implodes, right?

Your characters can never attack on your opponent’s turn, even if a card seems to say otherwise. Same rules apply even in the event of a galactic implosion and resulting gravitational chaos.

What happens when I reveal Bolster to play an Emergency Barricade or Crystal of Power?

If, when defending, you reveal Bolster to upgrade a character with an Emergency Barricade, it will remain on them until the next time they defends. This is because the 'when defends' event has already happened before Emergency Barricade was played. If, instead, you had upgraded with Crystal of Power, it will remain until the next time the upgraded character battles.