Sorry, not sure where to put this, either Workshop or Suggestions, but I think it fits best in Workshop since the idea's very removed from the normal gameplay loop. I have an outlandish idea, but am not able to mod it in myself. At all. I don't know how to mod for this game.

You know how you're just one person fighting waves of enemies, yet the enemy side can have large groups of various fiends? Sure, your one guy is stronger than they are, but one person gets worn out over time, eventually falling, likely to a single large hit.
This new character idea turns this game on its head, by having it so you're playing with a group of individual characters combating the hoard of enemies.

The Party.
The main mechanical change is that you now have a whole team of different characters to fight those waves of enemies with. Generally, they're less powerful than the normal cast individually, but are stronger when working together. Playing cards is changed to accommodate: whenever you play a card, you hand it to which of your soldiers to use that card, then select a target. This will spend that one character's energy, but not deplete the others' energy meters. Power cards, I'm not so sure about those, but they should probably affect the whole party. Finally, at the core, enemies will randomly target individual teammates, or at least with moves that only affect one target. Modifying the move pools of enemies to target all your party members will be required, just as having your own cards that allow you to target multiple or all enemies.
There are more technical details to make this work. When you begin a new run, you begin with a party of three mercenaries randomly chosen from a pool of available classes, so you're not always consistent with this increase in power. Each of them have different properties in max health, some having more or less health than others (but they all have less health overall), and each bring their own starting relics and starting cards to your run. However, to offset having effectively tripled your action economy, all of their cards are more expensive or less efficient when at one cost. These increased costs are mitigated by card effect conditions that depend on your team's combinations to recycle energy, like Uppercut and Dropkick, or with cards that are preferred to be used by a specific one of the classes. The whole pool of The Party's cards is available to add to your deck, and any one of your characters in the party can use the cards you draw, but some of the cards really prefer to be used by one class or in a specific sequences between classes for stronger effects than if used by another class or individually.
You don't lose your heroes forever when they're defeated, that wouldn't be great, and also your party's open to new members to join their quest. Whenever you clear a floor, your boss relic options can include one that upgrades your current band's starting relics or take on a new starting relic which will add the class who owns it to your growing party (but you also take their starting Strikes, Defends, and bonus starting card into your deck, too). Additionally, rank-ups with The Party grants new classes to the pool, their starting relics in their boss chest pools, and those class' cards. If one of your party members is defeated, they're out until you rest at a camp fire or clear the floor, or other events or even rare card can revive them. Otherwise, when defeated, they're untargetable and cannot play cards. You only lose the run when all your team members are defeated.
As the whole, and as previously mentioned and to avoid granting too dramatic of an increase in action economy, The Party's standard Strikes and Defends cost two energy instead of one to do the starting 6 damage or 5 defense. Sneko Oil's probably a little more valuable as a result.
A list of proposed classes to have available to The Party:
The Fighter, your baseline class and he just wants to do consistent damage. To start, he has 40 max health, a starting relic that offers the party some post-combat health regeneration, and adds an Attack card to your starting deck that is a variant of your standard Strikes with a clause that reduces its cost from two to one if another teammate played an Attack last, for everyone because The Fighter is just that cool. He brings pizza and soda to the table.
The Hex, your status-centric partial damage dealer. Maybe has 35 health? Relic begins each combat by inflicting a temporary status (more towards Frail than Weakness or anything else) on one random enemy, and brings an Attack card that deals damage penalizes that enemy with the clause that the penalty lasts longer if used by this class.
The Cleric, your team support that focuses on sustain. 35 HP, relic grants improved healing at campfires (something like a flat +7 health), and brings a Skill card that grants defense but also grants light healing to the whole group when used by this class.
The Mage, a team support that grants more influential swings. 30 HP, relic grants a status for a temporary +50% damage bonus on the turn after gaining defense from card like Defend, and starts with a Power card that grants Strength or Dexterity, or both if he uses it.
The Braggart, a damage dealer that likes to spice up the battle and show up the competition. 35 HP, relic makes it so unspent Energy between turns (useful where your characters have 3 energy but basic moves cost 2) grants temporary +1 Strength for the next turn, and has a starting card that attacks a random enemy X times at X cost, but is more efficient if he uses it, like increased damage or hits X+1 times at X cost for him.
The Stonewall, a defender that covers for his allies. 50 HP, a relic that grants five defense on the first turn, and a Skill card that grants good defense and will apply a temporary status that forces enemies to target him when he uses it.
The Interceptor, a pin-point assassin that works a thankless job. 35 HP, a relic that modifies enemy's random targeting to prefer the character with the most health, and brings in an Attack card that, if he uses it on an enemy targeting one of the other teammates, grants that ally defense.
The Highwayman, a gambling economy support. 30 HP, relic grants the Thievery status, and starts with a Curse card named "Double Blind" that reads "Costs 3. Ethereal. When this card is Exhausted, lose 60 gold. Grants +1 thievery for one turn. Then, if played by the Highwayman, additionally deals 2 damage to all enemies." Should be fun.
And there's more, just be creative to unlock the rest, there's a lot that can be done. And it'd be neat that, if this ever comes about, others could modify additions to the pool of classes to increase the options further. Having three or more characters offers a different design space than just the one character that wants to use a lot of moves per turn, and both still want to fish for energy cost reductions to improve economy.
So yeah. Lantern will be three times as strong, maybe nerf that one specifically for The Party as "starting each battle, one random teammate gets +1 energy." Curses and Statuses like Burn will be thrice as harmful.