Ahh yeah, Mist-Fuelled recovery. You can indeed shuffle any hero's deck into their trash, but only Nightmist recovers the hp. So of course, you'd want to choose the hero who's got the biggest trash pile, as long as they don't mind (eg probably best not to do it to Tachyon when she's been saving up for a Lightspeed Barrage ;)).
Sooooooooo… which of the 2 heroes is it? I have had very limited exposure to IR (First game with it last night!) and didn't see anyone with huge teammate healing potential, even looking through the decks I didn't see any high healing cards.
Well, the Argent Adept can heal, but the song that lets you do so I think heals up to five heroes for only 1hp. He has a one-shot which also heals all heroes for 1hp.
Nightmist, however, is my favourite character for a reason :D. She has two methods of healing herself (but only herself, not other people). Firstly, it's important to note that all of her cards have a value between one and four, given in a small box in the bottom right corner of each card. This is important for using pretty much all of her cards/abilities. Her first method of healing involves one of her Relics (equipment), the Starshield Necklace. With this equipped, at the end of her turn ("End phase") you can discard one card in order to regain that card's value in hp. Her second method of healing is the very amazing Ongoing card (limited, so you can only have one out at once…she only has two in her deck anyway) "Master of Magic". With this, every time you play a "Spell" card, you regain that card's value in hp. Nightmist has four Relics, three Ongoings, and I think only one normal One-Shot. All the rest are "One-Shot, Spell". So you have a lot of healing cards right there ;).
It's sort of important, as a lot of her abilities involve dealing herself damage - her innate power is "Nightmist deals herself two damage. Draw two cards", and there's also a Relic (the Elder Ring) which increases her damage by one. So she'd be hitting herself for three just with her innate power. A lot of her cards say stuff like "Reveal the top card of your deck. Nightmist deals herself and one other target that much damage". But you have the Amulet of the Elder Gods (another relic) which is pretty epic. The first time you'd take damage every turn you can discard two cards to redirect it to a target of your choice. One of Nightmist's spell cards is called Oblivion. With this one, you reveal the top two cards of your deck. First, every target takes damage equal to one of those cards' values (your choice), so of course it's better to choose the lower value one so you don't hurt your friends too much. Elder Ring will of course increase this damage by one. And if you've got your Amulet out you can discard two cards to redirect the damage that would hit you and instead hit one of the enemies twice (because the enemy would already be taking a hit anyway). Then you look at the other card you revealed and do that much damage to all non-hero targets. So if you redirected your damage the first time, some poor mob is gonna get hit three times, for anywhere between one and five (depending on whether or not you have the Elder Ring out) a hit. And that's just one card :D.
Anyway, I've never lost a game when I've played Nightmist. And I usually have at least 15hp (out of 27) left at the end. I can remember on one occasion getting as low as about 5hp but healing it all back (to full) by the end of the fight (and winning) :D. Nightmist also has really good deck control - Astral Premonition (Ongoing) which lets you discard a card to look at the top two cards of a deck (any deck, not just the villain) and put one on the top and one on the bottom, and then there's Mistbound, which is a One-Shot Spell. All you do when you play it (after healing if you've got Master of Magic out ;)) is discard two cards. Then choose any deck you like and that deck can't play cards till your next turn. Take that, Matriarch/Chairman/anyone else who draws horrible cards >:).