I originally set out to make a Shadow spell with Overheal, because I thought that would be neat and different. That eventually evolved into "what if you get a bonus for not Overhealing?" It's kind of like Burden of Pride or a similar condition.

Flavor Text: "Increased the whole city's lifespan by around 300%."

'The tooth is he doesn't really produce much Ivory.'

Each Spirit mentions what minion it creates in their name. Each Spirit vanishes from the game when Fergus dies, gets moved back to hand, shuffled in the deck or transformed.

Overheal is a mechanic with a lot of potential design space and this is one such method of that. Even though Overhealing is a way to mitigate lost healing and give you more board impact for using your healing abilities, it is still costing cards and resources to do that, and lost Health is still lost Health so there should be more ways to help your excess healing build your board.

Embodiment of Light is a 6 mana 4/4 with two keywords that work well together. With enough excess healing though, you can plop it down for quite cheap and help make up for the lost resources and then some. Perhaps those AoE-heal cards actually become viable for healing?

This sidequest requires you to Overheal for a significant amount, but the payoff of a Tutor plus a significant buff should make up for that (it works similarly to Scavenger's Ingenuity but the delay balances it). Thematically, the Sidequest represents redeeming an Undead in the Light, drawing it and essentially casting Apotheosis on it.

Seems like you were having a nightmare about being OTKed from 30 Health. Here, here.

I thought it was fun to explore what the other Healing classes could bring to the table with the Overheal mechanic, via dual class cards.

This card also helps to mitigate the main issue people has with Priest Hero Power: being useless when their hero is at full Health. I mean, Overheal in general is meant to do that, but since this gives you Armor, it does it in a pretty literal way.