When using Glassjaw to summon Leadblow, if the latter activates it's effect, detaching Glassjaw to avoid it's destruction, this triggers Glassjaw's effect, adding a Burning Knuckler monster from the graveyard to the hand. However, I've been warned that this move isn't correct, since detaching Glassjaw for Leadblow to survive is a cost, and thus, Glassjaw can't activate it's effect. Am I facing a card bug or have I been fooled?

You get Glassjaw's effect if you detach at any time unless it is the damage step to make Leadblow survive a battle.

So you get it if you use Leadblow on a Darkhole for example but not if you want to survive a battle.

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Leadblow's eff is continuous meaning that detaching an XYZ material isn't a cost.
Same for Zenmaines, Gachi Gachi and Maestroke.
During the damage step, only effects related to ATK or DEF increase can be activated therefore starting a chain. Glassjaw's eff isn't related to ATK or DEF therefore his effect won't trigger.

I just dueled with my Burning Knuckler deck and Glassjaw can activate it's effect when detached from Leadblow, so it's a ruling bug. I also noticed something else: Spar can special summon himself during the main phase 2, after the battle phase, even if you attacked this turn. Spar's effect: "If you control a face-up "Burning Knuckler" monster(s), you can Special Summon this card (from your hand), but you cannot conduct your Battle Phase for the rest of this turn." Double bug, in my opinion.

Me and Metatron both said that, Glassjaw can activate his effect as long as it is not done in the damage step. I duel with my Bk deck all the time and Glassjaw cannot activate his effect when detached in the damage step if you have a replay showing that he does please post it.

You should read Spar's effect one more time. "If you control a face-up "Burning Knuckler" monster(s), you can Special Summon this card (from your hand), but you cannot conduct your Battle Phase for the rest of this turn."
For the rest of the turn. is stated at the end so you can use it if you have already battled and are in Main Phase 2. But if used in Main Phase you cannot battle.

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I forgot to add that part. When detaching Glassjaw from Leadblow so the latter can survive a battle triggers Glassjaw's effect. It shouldn't, since it's the damage step.
And well, I thought Spar's effect would work that way, but as you might have seen, I'm kinda clumsy when it comes to rulings and I wanted to make sure of my moves, because I play other yu-gi-oh games that function manually and I don't want to make (more) mistakes in there.

I have just done a test with 3 separate cases.

1.Glassjaw detach from Leadblow in damage step. Glassjaw effect procs.

2.Trick Archfiend detach from Zenmaines in damage step. Trick effect procs.

3.Gishki Shellfish detach from Maestorke in damage step. Gishki effect procs.

These 3 all have similar effects "When this card is sent to the Graveyard by a card effect" Glassjaw and Trick Archfiend are both non-mandatory so their effect should not proc in the damage step, but Gishki Shellfish is a mandatory effect so I believe should work in this step anyway.

With Glassjaw and Trick being new cards I have not found rulings for them in this situation, but with the rulings as it stands they should not be able to activate in the damage step when detached.

Thank you Palen for bringing this to light, Glassjaw was not able to do this in the past and must be a recent bug.

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I just dueled with my Burning Knuckler deck and Glassjaw can activate it's effect when detached from Leadblow, so it's a ruling bug.

Detaching from Leadblow is not a cost, therefore Glassjaw can activate its effects fine.

I forgot to add that part. When detaching Glassjaw from Leadblow so the latter can survive a battle triggers Glassjaw's effect. It shouldn't, since it's the damage step.

Per ruling, the effect of Glassjaw can activate its effects during the Damage Step.

Spar can special summon himself during the main phase 2, after the battle phase, even if you attacked this turn.

Not being able to attack is part of the effect, not a condition. So it's only applied after you Special Summon Spar.

I have just done a test with 3 separate cases.

These 3 all have similar effects "When this card is sent to the Graveyard by a card effect" Glassjaw and Trick Archfiend are both non-mandatory so their effect should not proc in the damage step, but Gishki Shellfish is a mandatory effect so I believe should work in this step anyway.

With Glassjaw and Trick being new cards I have not found rulings for them in this situation, but with the rulings as it stands they should not be able to activate in the damage step when detached.

Thank you Palen for bringing this to light, Glassjaw was not able to do this in the past and must be a recent bug.

Being mandatory or not has nothing to do with being able to activate in damage step or not.

Being mandatory or not has nothing to do with being able to activate in damage step or not.

http://yugioh.wikia.com/wiki/Damage_Step 

This begs to differ with you.

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http://yugioh.wikia.com/wiki/Damage_Step 

This begs to differ with you.

I mean if a card effect is optional does not mean it cannot be used on Damage Step.
Look all the searchers like Mystic Tomato, all of them are optional and you can just use it effect on damage step.
Look also armageddon Knight, Elemental Hero Shining, Redox Elemental Dragon,etc...
All of them have optional effects and can be activated during damage step.

Cards that say "when destroyed in battle you can do x" would be useless if you could not use them in the battle phase. The situation that we are discussing are cards that can be sent to the grave at any time to have their effects proc, via a different cards effect. So their effects miss their timings.

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The main problem we have here is that these cards we are discussing do not have cards in the game right now that do the same thing so we do not have an official ruling.

Edit!
I have found it! At last!
Jinzo returner and zenamines.
Anytime Jinzo returner is sent to the grave via zenamines protection ability you can use his effect, apart from if zenmaines uses his effect part way through a chain then Jinzo will miss time.
So from this we can infer that Glassjaw should get his effect when Leadblow detaches to protect from battle. My apologies for getting this wrong but with new cards we are never sure.

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BK RULISNGS
Burning Knuckler Spar
-Special Summong this monster from your hand does not form a Chain Link.
-Can be summon in main phase 2 after the battle phase
Quote:
Burning Knuckler Glassjaw
- If this card is destroyed by its first effect, a monster can attack a different target or attack directly.
- Its second effect targets
- You can activate its second effect during the Damage Step
- Its self-destruction effect does not form a Chain Link.
- Both its self-destruction and Salvage effects are Trigger Effects.
- If this card is sent to the Graveyard by a card effect activated during the Damage Step, you can activate its Salvage effect
Burning Knuckler Spar
- You can Special Summon this card by its own effect during your Main Phase 2 if you've conducted your Battle Phase.
Quote:
Burning Knuckler - Switch-Hitter
- Targets 1 "Burning Knuckler" monster in the Graveyard.
- You can Target and Special Summon a "Burning Knuckler" Xyz Monster in your Graveyard.
- During the turn you activate Switch-Hitter's effect, you cannot activate Copy Knight. You cannot chain Copy Knight to the effect of Switch-Hitter.
- You cannot activate Switch-Hitter's effect during a turn you activated Copy Knight.
Quote:
Burning Knuckler - Headgear
- If you control Final Attack Order and you have "Burning Knuckler - Headgear" in face-down Defense Position, if it is attacked by a monster with 1000 or more ATK, it will not be destroyed by that battle.
Quote:
Burning Knuckler Counterblow
- This card's effect can be negated by Debunk.
- Its effect can be used during Damage Calculation.
- Does not target.
- Banishing this card from your hand or Graveyard is a Cost.
Quote:
Burning Knuckler Leadblow the Bound Barbarian
- If you send Burning Knuckler Glassjaw to the Graveyard by this card's effect, you can activate its recovery/Salvage effect.
- If a Burning Knuckler would be destroyed during the Damage Step by a card effect, you can activate this card's effect.
- Its first effect is continuous. Its ATK gain effect is a Trigger effect.
- If this card has its effect negated by Forbidden Chalice, its ATK becomes 2200, then 2600 because of Chalice.
- If multiple Burning Knucklers would be destroyed, you can only detach 1 Xyz Material from this card to protect exactly 1 Burning Knuckler.
- Leadblow's effects can be activated multiple times per Chain.
-Its Detach 1 Xyz Material effect doesn't form a Chain Link.
- You can activate the Detach 1 Xyz Material effect during the Damage Step for Battle or Card Effects.
- This card's ATK gain effect activates during even the Damage Step.
Quote:
Number 105: Burning Knuckler - Cestus the Meteor
- Detaching 1 Xyz Material is a cost of its effect.
- This card does not target.
- The damage inflicted to your opponent is treated as Battle Damage.
Quote:
Number C105: Burning Knuckler Caestus the Comet
- Its Xyz Material burn effect is based on the field.
- If Xyz Material burn effect destroys a Set monster, no damage is inflicted.
- This card's destroy and inflict burn damage Xyz Material effect activates even if "Number 105: Burning Knuckler - Cestus the Meteor" is detached.

When Mystic Tomato is destroyed or any card that got its effect activated when it's destroyed by battle, its effect will trigger when it leaves the field meaning at the End Step, NOT DURING THE DAMAGE STEP.
A monster is destroyed during the damage step but only leaves the field during the end step.
If a monster's effect is: "When this card is destroyed by battle and sent to the graveyard" it means that its effect will only trigger during the end step AND if it's sent to the graveyard. If it's only "destroyed by battle", its effect will trigger whether it's banished or sent to the grave.

In the case of Zenmaines, Maestroke or Leadblow, it would either mean that it's a bug OR that their effects trigger during the end step. In that case whether it's mandatory or not, the effect will trigger unless it miss timing.

As for what Steeleagel said, please read more carefully the example used in the wikia:
http://yugioh.wikia.com/wiki/King_Tiger_Wanghu 

Wanghu's eff can only trigger if the opponent manages to summon thanks to an eff during the damage step which starts a chain. In that case, considering it's a chain, it doesn't matter what happens because anything can be chained to an effect (speed spell 2 or 3). Considering Wanghu's effect is obviously speed spell 2, that example is quite bad.

The only exception in the damage step with monster effects are flip monsters because their effects trigger at the end of the damage step.

BK RULISNGS

Burning Knuckler Glassjaw
- Its self-destruction effect does not form a Chain Link.
- Both its self-destruction and Salvage effects are Trigger Effects.

Copy pasting Phone rulings without read them is bad.
The first ruling is wrong and outdated.
If you know a little about this game, you should know that Trigger effects starts a chain.

Also why you post the phone rulings of all BK monsters if the discussion was only about Glassjaw.
Also instead of Phone rulings you sould just post the official ruling from the database.

But I never mentioned Wanghu? I just pointed to the damage step on the wikia which happened to have Wanghu on there. I linked to that as it does not say anything about this where effects could be used and is why I thought that Glassjaw should not be able to work in that situation.

As I posted earlier Jinzo-Returner works when detached from Zenmaines and I have found that it was a well used deck because Jinzo-Returner works when detached from Zenmaines when he is being destroyed by battle. This is no different than Glassjaw and Leadblow, if the aforementioned effect has been know to be allowed than the second should be as well. So there is no bug in the game.

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Actually that was referred to how you mentionned effects being mandatory or not because your post was quite confusing. Seems you already know how that stuff works anyway.

There is an easy way to see if the effect trigger at the end step, get any XYZ monster like Zenmaines with an XYZ material like Trick or Glassjaw and attack it with Catastor. Detach Glassjaw/Trick first and then the second one. If the effect of the first detached XYZ material trigger AFTER the second got detached, it means that their effects trigger at the End Step otherwise it would miss timing which would make sense and not make that situation an exception.

Also could you please indicate your source for Jinzo-returner's ruling ?

I just tested two Glassjaws on a Leadblow against a Catastor, I had to use a lance first else Leadblow would just beat over Catastor with its first attempt at destruction.
What happened:Used lance first to make sure Leadblow would only get back to 2200 so the test would work - Attacked with Leadblow - Catastor effect kicked in - Detached to save - Leadblow 800 increase attack effect kicks in - then before it resolves Glassjaw asks to activate his effect from the grave - Ths causes a chain with Glassjaw going first and then the 800 attack for Leadblow - Then it asks again to save Leadblow - Detach causes the same chain as above with Leadblow surviving with 3000 attack points after he has gained from the effect (due to the lance from earlier).

http://www.pojo.biz/board/showthread.php?t=1081837 

This is an interesting debate as there is no official ruling that I can find on this case, and Jinzo - Returner is the only card I can find that has the same text wording as Glassjaw and Trick Archfiend. Hopefully we can come up with an answer together and determine what should happen as I do play Bk quite a lot and don't want to cheat especially when they are released in May.

And a side note you cannot try Zenamaines with two Trick Archfiends in the same way as you can only have one of their effects per turn.

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Tour Bus ' effect is quite similar even though it can work as a cost.
So far, all the "exceptions" I met in Yugioh weren't really ones and had a certain logic based on the rulings.
I really can't manage to find an explanation about it except being a CKSS (Cuz Konami Said So).
Need more people to give ideas on that debate.