Magdalene's strong point is her vitality. Her naturally high health and her starting item, Yum Heart, allow her to survive more damage than other characters.
With her high number of heart containers, Magdalene can afford more deals with the Devil.
She can also take more advantage of sacrificial damage, such as with a Blood Donation Machine, Sacrifice Room or from Bloody Lust. The sacrifice room is especially powerful for her, capable of giving you a floor one Angel Room provided you're willing to use your Full Health pill.
In Co-Op, the Yum Heart will also heal Co-Op partners for half a heart when used.
Magdalene's biggest disadvantage is her low speed, which makes her more vulnerable to threats, especially from fast-moving attacks and homing projectiles. Look to get items that increase speed and avoid those that lower it further.
Once the Aprils Foolchallenge is completed, this disadvantage is rendered moot as she will start every run with a Speed Up pill.
With Repentance, Magdalene's combination of a fully charged Yum Heart and a Full Health pill allows her to step on a Sacrifice Room spike seven times, allowing her to potentially get two angel room items on the first floor. However, this will leave her with only a single red heart.
Birthright: Grants +1 Filled Red Heart. Increases HP Cap to 18 Hearts.
Items that trigger on player damage, such as Gimpy and The Virus, stand to see more action through Magdalene's high health.
Old Bandage will have a chance to drop a heart upon being hit, which may come in handy if Magdalene's low on health.
Placenta's regenerative abilities can further supplement Magdalene's self-healing. The same applies to Little C.H.A.D.'s red heart generation and other similar healing items.
The Wafer is helpful to Magdalene's health-driven play style.
Shielding items can be used to compensate for Magdalene's low speed. (Infamy, Holy Mantle...)
Abaddon removes all red heart containers, which can turn out to be a disadvantage for Magdalene.
Bucket of Lard's heart container bonus is tempting, though it's better to avoid this item initially as it would render Magdalene's speed very low. Any other speed down items are to be avoided as well (Taurus may make an exception from its speed increase over time and My Little Unicorn effect if the speed becomes high enough).
Dark Bum eats red heart pickups, which can dampen Magdalene's regenerative play style. However, used in conjunction with her starting Yum Heart, Dark Bum can be a powerful way to turn otherwise redundant pickups to your advantage.
If Dead Cat is picked up early, it takes away Magdalene's primary strength (high health) and exacerbates her biggest weakness (low avoidance).
There are some stray pixels on Maggy's "Bad Pill" animation.
Maggy appeared in the original Binding of Isaac.
Maggy's unlock requirements in Rebirth are the same in the original Binding of Isaac.
Magdalene's unlock requirement of having seven heart containers may be a reference to the "seven demons" that were driven out of Mary Magdalene.
Magdalene is the name of Isaac’s mother Magdalene O. Moriah, or MOM. The last name Moriah is a reference to the biblical story of Isaac where the name Moriah is the name of the mountain Isaac was to be sacrificed on in the Book of Genesis.
In the game files, the image file for Maggy's hair is named maggiesbeautifulgoldenlocks.png.
Maggy's hair appears to be identical to the wig that Isaac receives in one of his mid-floor nightmares.
The person with gold hair in ending 14 and the Final ending has been confirmed to be Isaac wearing a wig, which furthers this idea.
Another piece of evidence is that the four female playable characters all have Isaac's voice.
Magdalene's transition screen portrait.
Magdalene's locked character icon, depicting her in chains.