Here, you may ask any ruling, mechanics, or card interaction questions you may need resolved, and another teacher or I will answer them.

My question is regarding the 'Once per turn' in card effects. When does it include my opponent's turn? E.g LS Lumina, call of the mummy and dimensional alchemist can't activate in my opponent turn, while six samurai Shi-en, castle of the dragon souls, Quasar and cracking can be activated in my opp turn..

Loudfist wrote:

My question is regarding the 'Once per turn' in card effects. When does it include my opponent's turn? E.g LS Lumina, call of the mummy and dimensional alchemist can't activate in my opponent turn, while six samurai Shi-en, castle of the dragon souls, Quasar and cracking can be activated in my opp turn..

This requires knowing the difference between an Ignition Effect and a Quick Effect. Ignition Effects are Spell Speed 1 and can inherently only be activated during one's own Main Phase. Spell Cards such as Call of the Mummy have what are called Ignition-Like Effects, and work similarly to Ignition Effects.

Meanwhile, things like Shi En and Shooting Quasar Dragon have Quick Effects, which are Spell Speed 2. Being Spell Speed 2, they are allowed to be activated on either player's turn. Castle of Dragon Souls is a Trap Card, so it is already inherently Spell Speed 2; its effect to raise ATK by 700 is therefore Quick-Like as opposed to Ignition-Like.

To tell the difference, you can generally use PSCT, which will indicate on a Monster or Spell if it can be used on either player's turn or not. Some cards don't have PSCT though, so you would need to check rulings on that card (Yugioh Wikia is the best site for this) to see if it is an Ignition or a Quick Effect.

Alright i shall read on ignition and quick effects, thanks.

New question: If Player A controls Noble knight Medraut that is equipped with a noble arms equip card, and Player B uses Breakthrough skill to negate Medraut's effect, Player A chains MST and targets the Noble arms that is equipped to medraut. Would Breakthrough skill still negate Medraut altho he's no longer an effect monster?