When opening a chest, if it doesn't contain the ball, it explodes. As a result of that explosion the player must make an armor roll, and if broken, make an injury roll.

This should be an unmodified roll. It's not.

If the player making the armor roll has Mighty Blow, that is added to roll. Not sure if it's added to the injury roll if MB is not required to break armor.

This would appear to be a bug, and makes taking Mighty Blow on anyone likely to open a chest a big risk.

It's not a bug it's a miss interpretation of the rules

Well, thx for the report !

Rogue wrote:Not sure if it's added to the injury roll if MB is not required to break armor.

I just tried this in Hot Seat and the Mighty Blow bonus is only used and logged if it's required to break armour, or if armour breaks naturally (then it's added to the Injury roll).

Here's the log from my test where two Troll Slayers (with the same name) on opposing sides were standing next to an exploding chest. You can see both instances of Mighty Blow use.
| GameLog(02): TH1 #09 Grund Kazig-Troll Armour Value (9+) : 5 + 5 = 10 -> Success
| GameLog(02): TH1 #09 Grund Kazig-Troll Injury : 5 + 4 + 1 {Mighty Blow} = 10 -> Injured
| GameLog(02): TH1 #09 Grund Kazig-Troll Casualty : Fractured Arm -> Miss next game
| GameLog(02): TH2 #09 Grund Kazig-Troll Armour Value (9+) : 5 + 3 + 1 {Mighty Blow} = 9 -> Success
| GameLog(02): TH2 #09 Grund Kazig-Troll Injury : 4 + 4 = 8 -> KO'd

Here's a similar try where Might Blow does not appear as it would have had no effect:
| GameLog(02): TH2 #09 Grund Kazig-Troll Armour Value (9+) : 2 + 4 = 6 -> Failure
| GameLog(02): TH1 #09 Grund Kazig-Troll Armour Value (9+) : 6 + 1 = 7 -> Failure

This is a straightforward bug as there is no room for misinterpretation in the Mighty Blow skill description or the Opening Chests rules:

"Mighty Blow (Strength)
Add 1 to any Armour or Injury roll made by a player with this skill when an opponent is Knocked Down by this player during a block."

"OPENING TREASURE CHESTS
If the chest is trapped it explodes (remove it), and the player who opened it and any other players adjacent to the square it was in are knocked over and must make armour rolls to avoid injury."

This bug affects also bomb explosions. If a player has the Mighty Blow skill and is knocked down by a bomb exlosion, the skill gets used on the player himself.