Maggie the Immortal

[Filar]

It's possible to make Maggie immortal if you find a habit and still own her heart. Then everytime you take damage, the Maggie's item's (heart's) bar is regenerated by half. After it's fully regenerated you can use it to get one heart. It had worked at least until I won the game for first time. It was quite easy with such set, actually.

[That Havel]

yes it is, at least up until you get to the Womb/utero which then every hit will take one heart instead of half

[Dakota]

But then you find The Wafer.