Stealing Boss items
Crazy Armor
Steal: Galtite
Uses: Hien, Force Gloves
In its first stage, Crazy Armor will do a long-range attack where it will try to "headbutt" you. Go behind it and steal the item. You will have a good amount of time if you dodge it close enough to its body.
Wyvern
Steal: Shortcake
Uses: HP Restore
At the beginning of the battle, Wyvern will burrow its head into the ground. You must jump onto its body and stay on it while the Wyvern takes flight. You have some good time to damage it while it flies. About seven or eight seconds, steal the Shortcake from the Wyvern's neck. You will take no damage when you fall.
Trevor Belmont (Round 1)
Steal: None
Uses: None
Skeleton Diver
Steal: Sushi
Uses: HP Restore
Later in the battle, the Skeleton Driver and the Zombie Fish will jump onto the platform together and slide toward you. Dodge to the side, then jump and steal before they retreat to the water.
Minotaur
Steal: Devil Iron
Uses: Hien
Later in the battle, the Minotaur will leap and try to slam directly on top of you. It usually does this at long range. When it is far away, wait for it to jump, then run backwards a short distance. Then, double jump into its face to steal the Devil Iron. The double jump should be timed just before the Minotaur lands.
Isaac (Round 1)
Steal: Devil's Vein
Uses: Chavre-Souris (Isaac's signature lance, prerequisite to summon The End. Gather 100 Evo Crystals on your Brow ID to evolve)
Isaac will occasionally use the second attack's finisher (sliding, smash upwards) at long range. He usually does this at the beginning of the battle. Block or dodge the slide, then steal as he lands. To make things easier, use the Phoenix ID's Big Bang (kill a certain number of enemies level 25 or higher) attack to instantly kill Abel (Isaac's The End summon), as he does not count as a Boss. Big Bang does not affect Bosses.
Saint Germain
Steal: Immortal Fragment
Uses: Gatling Gun
Keep a strong Mage-type ID out. Occasionally, Saint Germain will freeze time and hit you with a giant slash or explosion attack. Using Time Stop while time is frozen cancels out the freeze altogether and will allow you to steal the item.
Trevor Belmont (Round 2)
Steal: Curry
Uses: HP Restore
Trevor uses a more powerful version of the Cross Heart weapon (the regular one is the boomerang), where he leaps in the air yelling "Holy Cross!". Immediately after he lands, but before the light fades, steal from him.
Dullahan
Steal: Purple Glitter
Uses: Laser Blade (Isaac's weapon in the introduction sequence and second Boss battle)
Be very careful doing this, because making a mistake will cause you a lot of damage. At the beginning of the battle, he will leap into the air and send out a multi-hit shockwave. This opens the steal window. To get him to do it up close, block or Perfect Guard his sword attacks. Occasionally he will use a rush attack similar to the Great Armors in Eneomaos Machine Tower -- be on the defensive. When he does the leap, do a normal jump and steal from him. If you are too far, delay your second jump or jump over the first hit and Perfect Guard the second.
Isaac (Round 2)
Steal: Cheese
Uses: HP Restore
Isaac is very different the second time you fight him, and seems to be lightweight. Equip a fast weapon like a Bastard Sword or a Laser Blade (if available), or a Knuckle-class weapon. Use the first finishing move to send Isaac flying across the room. Do it near a wall, and quickly press the button to steal, as he must be airborne.
Death
Steal: Death's Pulse
Uses: Death's Scythe (strongest weapon in the game, because of the sheer difficulty to get this item)
First, make sure you are experienced with your Perfect Guards. When fighting Death, have a Fairy-type ID summoned. After losing the first lifebar, Death will sparingly (perhaps twice in ten minutes) use a Supernova attack. He will condense a fireball in his hands for a brief moment, then throw it out onto the battlefield. Stay next to Death while he does this and prepare yourself. Block the first hit from the Supernova, then proceed to Perfect Guard the rest of the hits, which are in a specific rhythm. If one is accidentally guarded, then you have one chance to Perfect Guard the next. If you do not, you must to start over. Jump into the air after the last hit, but before the fire dissipates and steal. The window will open, then close, but the game will acknowledge that you have Death's Pulse. Fortunately, Death occasionally does this attack twice in a row, if you should fail the first time.
Legion
Steal: Pizza
Uses: HP Restore
Fight Legion using a longer range weapon with decent speed, like the Chavre-Souris or the Laser Blade so you can take out both Legion and the corpses that will do heavy damage to you. Also, use a flying ID, like a Crimson or Indigo or The End. After its shell collapses entirely, get on a ledge higher than it. You have approximately 12 to 15 seconds to move to a higher point. Take a free fall into Legion when it glows with a malevolent purple aura. Time the steal to take the Pizza in mid-fall. Quickly run to the edge of the room to avoid Legion's final shell from crushing you and prepare for Legion's second form.
Nuculais
Steal: Napoletana
Uses: HP Restore
Nuculais is the game's ultimate optional Boss. It can kill you very quickly. It has a laser that will kill you in less than ten seconds if you are less than level 50. It also has a telekinesis attack that will throw exploding corpses at you, a liquid-teleportation attack that damages you, a series of slaps, a flying sword dash, and a giant-transformation move. However, the move to look for is a grab attack. He will rear his arm back and then forward, extending at you. Perfect Guard the attack then rush him and steal.
Dracula (Round 1)
Steal: Tomato Juice
Uses: HP Restore
Dracula will open a pair of demonic wings and disappear, saying "I'll burn you to ashes!" He will then reappear for a grab attack that does serious damage. Dodge or jump away when he reappears and steal from his face. He does this attack quite often.
Dracula (Round 2)
Steal: Vampire Blood
Uses: Dracula's Clothes (great armor)
Dracula is now a huge vampiric black angel. Occasionally but rarely, Dracula will back away and rush the platform with a huge destructive punch. After he does it, jump into him and steal from his chest. The punch is easy to avoid, but a shockwave follows it which will mess up the steal and do serious damage. You can double jump the punch and the wave, or use the Fairy-type Tiramisu's Invincibility Jar technique.
Boss Rush mode...