The new Major Shockwave card raises the question: what officially qualifies as a "Decepticon card" or an "Autobot card"? Is it just the presence of either symbol behind the battle card text?

Yes. The faction symbols as well as the different frame/treatment at the top and above the Battle Card text for each faction.

Source: Wizards of the Coast (2019-04-22)    【Link to Ruling】

Tags: Factions

If Mounted Missiles in the armor slot can you scrap it with a bashing shield?

No, it is still a weapon even though youve put it in the armor slot.

Source: Wizards of the Coast (2019-04-22)    【Link to Ruling】

Tags: Mounted Missiles

I have Optimus Prime - Battlefield Legend and an untapped partner bot on my side. I attack with Optimus in bot mode. One of his flips is Swap Missions. If I elect to play Swap Missions, Optimus untaps and my 2nd bot taps. What happens next? I argued Optimus was still the attacker even though he is untapped, so combat with him should proceed. My opponent argued the other bot was now the attacker since only a tapped bot can attack (since the two "swapped" missions), then utilizes the earlier flip's battle icons.

The first suggestion is correct in this scenario.

Source: Wizards of the Coast (2019-04-22)    【Link to Ruling】

Tags: Swap Missions

I found a How-to-Play guide that states "After a round is over, the player who tapped all of their characters first becomes the first player for the next round. You untap all characters and the next round starts with the first player. This continues until one player wins by being the only player with characters on the board."
If this is in fact how the turns work, if I tap Metroplex for an attack and get his ability off, Metroplex will be tapped first, then all my opponents bots will tap letting Metroplex go first next round. Or is it still turn-based as Metroplex taps all opponents bots? Metroplex's players turn ends and then everyone untaps and it is now the opposing players turn?

This is not technically how the rules work. There are no rounds in the Transformers TCG. When your turn is over, it is then your opponents turn. Please see the official rules here for further details.

Source: Wizards of the Coast (2019-04-22)    【Link to Ruling】

Tags: Play

I play Peace Through Tyranny and then attack, me and my opponents now have no untapped characters. Do we untap everyone, my turn ends and then I get the next turn?

Yes.

Source: Wizards of the Coast (2019-04-22)    【Link to Ruling】

Tags: Peace through Tyranny

If I have Static Laser of Ironhide equipped to Ironhide when I combine the Sentinels into Optimus Maximus, and keep it, does he take the damage penalty, or does he count as Ironhide since Ironhide is part of him?

Optimus Maximus is not Ironhide, so he would take the damage.

Source: Wizards of the Coast (2019-04-22)    【Link to Ruling】

Tags: Static Laser of Ironhide

Do blue or orange battle icons stick around for additional attacks with or on the same character in the same turn?

No. They are only used during the battle in which they were flipped.

Source: Wizards of the Coast (2019-04-22)    【Link to Ruling】

Tags: Battle Icons

During the draft process, a draft member drafts character cards that add up to 25 stars. Then during the process for the battle cards, the same member acquires four battle cards that are 1-Star value. What is the procedure for this? Does the player take damage equal to the stars over 25? Does the player play a deck that is 24 cards?

In this scenario, you would have to play one fewer character to compensate. We would recommend avoiding this if at all possible.

Source: Wizards of the Coast (2019-04-22)    【Link to Ruling】

Tags: Draft Rules

Combiners retain until-end of-turn-effects even after they combine, but what happens with effects that impact more than one character? For example, if I have 3 Sentinels in play and I flip Ironhide - Steadfast Brawler in the KO area to give them all Pierce 2 and then combine, does Optimus Maximus have Pierce 2 or Pierce 6?

In this scenario, Optimus Maximus would be granted Pierce 6.

Source: Wizards of the Coast (2019-04-22)    【Link to Ruling】

Tags: Combiner

I was looking for clarity on when triggers occur during the window when attackers and defenders are declared. Can Debilitating Crystal bounce Security Console before it gets to trigger?

Choosing the attacker and which character its attacking is a single step. After that, any abilities that trigger when a character attacks (but dont refer to whats flipped) happen, followed by any abilities of the defender. In your scenario, Debilitating Crystal would not bounce Security Console before it triggers.

Source: Wizards of the Coast (2019-04-22)    【Link to Ruling】

Tags: Debilitating Crystal

If I play Hunker Down while Megatron - Living Weapon has a weapon in his armor slot, do I have to replace the weapon with an armor from my scrap pile, or can I choose not to?

If you are able to, you must replace the weapon with an armor.

Source: Wizards of the Coast (2019-04-22)    【Link to Ruling】

Tags: Megatron, Living Weapon, Megatron, Living Weapon

If Optimus Prime - Battlefield Legend attacks with Power Punch. And flips over Swap Parts you move all upgrades to another character does Power Punch/Grenade Launcher destroy itself?
No, after the battle, you check, and the upgraded character is not the one who attacked, so it would not scrap itself.

Source: Wizards of the Coast (2019-04-22)    【Link to Ruling】

Tags: Optimus Prime, Battlefield Legend, Optimus Prime, Battlefield Legend