I. Start Step
The Start Step is pretty straightforward. It's when you or your opponent enters the Battle Phase. You can activate Quick-Play Spells and Trap Cards at this time.
Standard Fast Effect Timing applies here, where the Turn Player (TP) is given priority to activate Traps and Quick-Play Spells, and if the TP passes priority, the Non-Turn Player (NTP) is given an opportunity to do the same.
So, what can you actually do here? In fact, you can do quite a lot! You can activate Threatening Roar during the Start Step of the Battle Phase instead of when you leave Main Phase 1 to prevent them from doing things after you activate Threatening Roar. You can also use the Start Step of the Battle Phase to activate things like Compulsory Evacuation Device on Star Eater in order to get around its invincibility effect.
When you are about to activate something at the end of the Main Phase, reconsider if you can activate it during the Start Step, since if you activate it at the end of the Main Phase, your opponent is given another chance to activate things.
II. Battle Step
The Battle Step is when the TP can declare an attack. Once an attack is declared, the TP retains Priority to activate effects, like the effect of Number 39: Utopia. When the TP passes priority, the NTP is given a chance to respond to the attack with cards like Dimensional Prison, Mirror Force, and Magic Cylinder. Note that there is only ONE chain in response to an attack, and cards like the aforementioned Mirror Force can be placed anywhere on the chain and resolve with the intended effect.
Example: The TP controls Elemental HERO Voltic, Elemental HERO Neos Alius, and Elemental HERO Bubbleman, and the NTP has an Atlantean Marksman. Elemental HERO Neos Alius attacks the monster and the TP activates Super Polymerization in the Battle Step, Special Summoning Elemental HERO The Shining with Voltic and Bubbleman. There cannot be any more responses to the attack in the Battle Step.
If, in the previous example, Super Polymerization had targeted the Atlantean Marksman and a HERO to summon a Elemental HERO Absolute Zero, since the number of attack targets has changed, a Replay occurs, and the attacking monster may still declare an attack. If it elects not to attack, then that monster cannot attack for the rest of the Battle Phase.
Slightly more relevant example: The TP attacks with a monster, and passes Priority. The NTP activates Mirror Force, and the TP chains Seven Tools of the Bandit. The NTP can't activate his set Dimensional Prison anymore, since there is no window for it to activate.
However, note that the Battle Step doesn't end when that chain resolves. Traps, Quick-Play Spells, and Quick Effects can be activated normally, but cards that respond to attacks can no longer be activated. When the TP and the NTP both pass Priority, then you proceed to the next Step.
III. Damage Step
There are 7 substeps of the Damage Step. Only specific cards can be activated during the Damage Step, and these are:
Counter Trap Cards (Seven Tools of the Bandit)
Spell Speed 2 Effects that directly alter the ATK/DEF of monsters, like Fire Formation - Tensen
Effects that have activation timings, unless they specify otherwise, such as Madolche Ticket
Quick Effect that negate (and only negate) the activation of a card/effect, such as Herald of Perfection
Some cards are ruled to be able to activate in the Damage Step, but they're not exactly meta-relevant, so I'm gonna skip them. In each of the substeps, the numbers (1, 2, 3) denote the order in which things are applied.
A. Substep 1: Start of the Damage Step
Apply Continuous Effects of Monsters, such as Jain, Lightsworn Paladin.
Monster Trigger Effects activate, like Neo-Spacian Grand Mole. If something like an opponent's Ally of Justice Catastor activates, SEGOC applies.
You can also activate effects that directly affect a monster's attack, like Fire Formation - Tensen
B. Substep 2: Flip a face-down monster face-up
If the monster being attacked is face-down, flip it up. Flip Effects and Trigger Effects do not activate at this time.
If the monster has a continuous effect as long as it is face-up, like Jinzo, it is applied.
Again, you can activate effects that directly affect a monster's attack, like Fire Formation - Tensen
C. Substep 3: Before Damage Calculation
Cards like Ehren, Lightsworn Monk activate here.
Cards that are flipped in Substep 2 and have effects that are applied without Damage Calculation activate here. Blast Sphere is an example.
Again, you can activate effects that directly affect a monster's attack, like Fire Formation - Tensen. There can be multiple Chains for these.
D. Substep 4: During Damage Calculation
1.There is only one chain during Damage Calculation. Quick Effects that negate the activation/effect of a card/effect which have to chain directly to the activation/effect they wish to negate, such as Herald of Perfection or Photon Strike Bounzer. Cards that modify ATK/DEF cannot be activated unless specifically allowed (Prideful Roar). If a monster is destroyed in a chain during this substep by something like Divine Wrath, the chain resolves and damage calculation stops, and no battle damage is inflicted and no monsters are destroyed by battle.
Honest and Injection Fairy Lily are special in that they can activate in Damage Calculation. There are various rulings and situations regarding them, the ones below are the more pertinent ones.
Honest vs Honest/Crane/Kalut/whatever
TP controls Jain, Lightsworn Paladin, and NTP controls Bujin Yamato. Jain attacks, Honest activated in Damage Calculation, and NTP chains Bujingi Crane. Crane resolves first, Jain gains Yamato's new attack, and wins the battle. Make sure you analyze the chain carefully if you predict multiple damage calculation modifiers.
Injection Fairy Lily and Skyscraper
Elemental HERO Absolute Zero attacks IFL, and in Damage Calculation, IFL activates to boost its attack to 3400. After IFL's effect resolves, Skyscraper's continous effect is applied to boost Elemental HERO Absolute Zero to 3500 ATK.
E. Substep 5: Battle Damage
If something like Giant Kozaky was flipped up but not destroyed by battle, it is destroyed.
If Jinzo is destroyed, its Continuous Effect is no longer applied.
Flashbang has priority here.
Cards that activate when Battle Damage is inflicted, like Kycoo the Ghost Destroyer, Spirit Reaper activate. Red Dragon Archfiend also activates.
F. Substep 6: Resolve Effects
Flip Effects activate at this time. Cards like Geargiarmor also activate here.
Trigger Effects like D.D. Warrior Lady activate here.
G. Substep 7: End of Damage Step
Monsters are destroyed and sent to the Graveyard. Stuff like Blackwing - Shura the Blue Flame, Jurrac Guaiba, Apprentice Magician, etc. will activate.
Effects of cards like The Six Samurai - Zanji activate.
If you have another monster on the field, you can return to the Battle Step and declare a new attack. Remember that you can only declare an attack one at a time.
IV. End Step
Once you're done with all the Battles by repeating the Battle Step and Damage Step, we reach the End Step. Some things that activate here include standard Trap Cards, Quick-Play Spell Cards, and stuff like Galaxy-Eyes Photon Dragon or Gladiator Beast effects. As noted in the PSCT Article (which you all should read), if you have multiple effects to activate (such as the GBs), they activate and resolve on different chains, and are not chained to one another.
In conclusion thank you for reading this. I do not want to be given all the credit since I did not make all of this, a friend of mine did and i only helped.
This is my first topic and I hope you all learn something!
Tue Apr 28, 2015 6:22 pm by 
Subject: Battle Phase Mechanics 
heheh didn't kno you sux the.......ha. 
