A monster with '?' ATK will be treated as having an ATK of '0' while it is face-up on the field, if no effect is currently giving it an ATK value. It will have 0 ATK for the purposes of Damage Calculation, and for any card that affects monsters below a certain ATK.
No, it doesn't end the battle phase.
Yes, Stardust Dragon can activate its negation Quick Effect in the Battle Phase, and even the Damage Step.
Standby phase is in a yugioh duel after draw phase,you could use card effect at standby phase.
Yes, of course. There's no reason to think he can only attack monsters that were present at the beginning of the battle phase, or before his first attack is declared. If monsters are summoned during the same battle phase, by any effect, he may attack them.
Magical hats can only be used during your opponent's battle phase. Seeing as they can't flip their monsters during their battle phase, no. However, if your opponent does activate a spell or trap card during the battle phase, you can use Magical hats and protect your monsters. Overall, yes. You can use magical hats to protect your monsters from targeting effects as long as it's during your opponent's battle phase.
Yes, Battle Fader's effect is a trigger, activated in hand when an opponent's monster declares an attack. Light and Darkness Dragon will chain to and negate this, meaning Battle Fader is not summoned and the battle phase does not end. Note that Light and Darkness Dragon does not destroy the cards it negates, so Battle Fader will remain in hand. It can be activated again when the next attack is declared.
their really isn't a big difference between them except for the fact in Main Phase 2 you can't attack again if you are planning on setting Spell [S]/ Trap [T] cards face-up or face-down. what i mean is - Draw Phase - Main Phase 1 - Battle Phase - Main Phase 2 - End Phase during Main Phase 1 you can set your s/t cards and launch you attack in your battle phase. Main Phase 2 if you can set more s/t cards after your done setting the amount you want to set you'll probably have to end your turn.
It lasts every end phase.
Yes, of course. Exactly the same as main phase 1.
Polymerization is a spell speed 1 card. You cannot activate it in your battle phase at all.
Galaxy Eyes Photon Dragon has absolutely no protections against being destroyed, apart from its battle phase banish ability, which can only be done at a specific part in the battle phase. So any monster destruction will do it - Exiled Force, Fissure, etc. You could use a card like Divine Wrath against its Quick Effect, if it tried to banish itself in the battle phase to escape destruction from a card like Mirror Force.
Cyber Dragon Zwei gains a 300 ATK bonus during the Damage Step only, in a battle when it is the attacking monster. As soon as you leave the damage step, it loses the bonus.