I'm actually interested in exploring using such a system for the main game (akin to Dark Souls new game+). That is, being able to infinitely scale the game, maybe obtaining some manner of currency based off completion % for each run that can be used for purchasing silly things!
That encourages tediousness, doing the same thing over and over each run in order to acquire tokens. People will pick the most efficient build to speedrun the game and acquire those tokens, since it's getting increasingly harder. It will get boring and quickly for most, though I probably wouldn't mind it - it'd be an excuse to try to optimize a build. I think I suggested it a while back, but I think an objective-based NG+ mode would be most well received. Especially in terms of encouraging different playstyles of the game, getting the most of what it has to offer by playing in ways they might not normally.
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You've beaten Secrets of Grindea! What now?
A box pops up at the end of the game, congratulating you and informing you that you have unlocked NewGame+ options. Check them out on the main menu!
So you go to the main menu and see the new NewGame+ Objectives. You select it and see a long list of new ways to play the game, a token count earned on the side and a token store beneath it for things to spend tokens on. Many objectives are greyed out with a message of "Complete # Objectives!" to display them. Initially you would see a list like...
Beat The Game: You did it! Objective complete.
Victory Lap: Select a completed save file. Choose this objective to start from the beginning with all your levels, items, cards and gold! Nothing stands in your way!
HARDER!: Select a new save file. Choose this objective for all enemies to gain increased DMG, HP and attack speed. When this objective is completed, it becomes
HARDER!!, then
HARDER!!! and so on with increasingly high enemy stats and a new token each time.
Two To Tango: Select a new save file. Monsters are always balanced around two players, and boss rooms may only be entered with two people.
Three Musketeers: Same as Two To Tango, but for three.
Quartet: Same as Two To Tango, but for four.
Firestarter: Select a new save file. Begin with 1 skillpoint. Your weapon attacks do 0 damage, you may only choose fire spells.
Frostcaller: Same as Firestarter, but ice spells.
Earthquaker: Same as, but earth spells.
Windbreaker: Same as, but air spells.
I Like Swords: Select a new save file. Begin with 1 skillpoint. Your weapon attacks do 0 damage, you may only choose 1H skills. (Clones from Shadowclone will do damage as normal.)
I Like Bigger Swords: Same as I like Swords, but for 2H skills. (If Berserker Mode is active, weapon attacks do damage as normal.)
Ping-Pong: Select a new save file. Begin with 2 skillpoints. Your weapon attacks do 0 damage. After using a melee skill, melee skills are locked until you use a magic spell and vice versa. (Ex: Dash -> Fireball -> Spirit Slash -> Earthspike, etc)
By Your Powers Combined: Select a new save file. Begin with 4 skillpoints. Your weapon attacks do 0 damage. After using a fire spell, you must use an ice spell. After ice, earth. After earth, air. After air, fire.
Genocide Run: Select a new save file. Enemies no longer respawn. If you leave a screen without clearing the enemies, they won't be there when you return. If you die during a wave-based room of enemies, you receive no EXP or drops from enemies when re-attempting the room.
Pacifist Run: Select a new save file. Your attacks do 0 damage, spells and skills are locked out. Only support spells are available. Touching enemies with your shield gradually drains their HP. Perfect guarding removes a chunk of their HP. You acquire no experience, but your HP increases after each boss.
Scavenger: Select a new save file. All shops are closed, side-quests unavailable and non-vital chests are empty. You may only use equipment you craft or acquire as an enemy drop.
I Choose You: Select a new save file. Begin with 1 skillpoint. Your weapon attacks do 0 damage. You may only choose Frosty Friend, Cloud Strike and Summon Plant as skills.
31337: Select a new save file. All monsters are elite.
Untalented: Select a new save file. You receive no talent orbs.
And then more difficult ones, that appear after after you've completed a number of the above ones.
Time Attack: Select a new save file. A timer appears on the screen at all times, with a goal next to it. If you fail to complete the goal in time, you receive a Game Over and reset back at the start of the game with nothing. The goals are 'Beat Gigaslime before #', 'Clear the first temple before #', etc.
The Basics: Select a new save file. The only equipment you can use are Wooden Sword, Big Branch, Wooden Shield.
One-Hit Wonder: Select a new save file. You have one hit point.
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So when you select a completed or an empty save file, you'd see 'Objectives' as an option to choose from and the option to pick one. Or multiple ones, if you think you can mix-and-match multiple in a single run (and they're actually able to be combined, like Firestarter+Untalented+31337.)
This seems like it'd greatly extend gameplay time with only small changes made for a lot of these.