From simplest to most complex:
- Reverse the slider at the end of the bar rather than restarting it.
- Change the zone location and distribution per enemy
- Add new kinds of zones into the pool with various special effects
- Procedurally generate zones based off of past generations in accordance with some type of story-telling balance system ala Amorphus+ et al. At the simplest level, reuse only previously-seen zones until its time to introduce a new one and separate zone options into tiers, delivering an option from the correct tier based on total round number using a cycling structure like t1 t1 t2 t1 t1 t2 t3 t2 t1 t1 end, for example.
- Add a non-combat system part of the game, for example (in similar order):
- Add an overarching plot
- Have that plot delivered incrementally rather than in one opening and closing screen-card, with updates between some/most battles.
- Add encounter-specific game over text
- Add encounter-specific text variations related to things like the player winning with hp over or under a certain threshold, the fight taking more or less than a certain amount of time, etc.
- add graphics for the enemies and cutscenes/dialogue.
- allow the player some optional choices with a small amount of impact on the game, for example some optional levels that unlock a second ending.
- allow the player more robust choices, such as (in order again):
- optional sidequests that don't meaningfully impact the plot
- a relationship system with npcs approving or disapproving of pre-determined choices
- general systems in which the player acts and in which individual choices are categorized, so that npcs approve or disapprove of categories of behavior rather than specific acts.
- character-specific quests
- character-specific ending modulation (ala Fallout New Vegas)
- sidequest/main-plot integration
- have no characters that cannot be interacted with as NPCs.
- Add a map on which a player avatar moves when not in battle
6. allow the player to interact with/affect the game mechanics (e.g. zone distribution and effect, slider speed, slider number), e.g. by equipping items or receiving boons
7. Reflavor the combat system to be something other than physical violence.
8. Add additional combat systems and logic to switch between them (e.g. based on enemy type, or based on choosing a random one each level)