There were so many ideas submitted on the mana redesign that I really had to take a step back to collate all the data and come up with a few discrete options that I feel like are viable alternatives to the way things are done now. I'm still mulling what I like best, but I thought I'd put a poll out here just to see where other people's heads are at.
MANA RECHARGE DIFFERENCES FROM CURRENT DESIGN
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1. Mana potions and mana scrolls are completely removed from the game.
2. Mana fully recharges from 0 mana to full mana over the course of maybe 20 seconds for an average character (but character stats would cause this rate to vary). Mana only recharges when your character isn't using spells that cost mana.
3. Uber-powerful spells that would be implemented would simply have a really long cooldown to offset their being constantly spammed.
4. Spell scrolls would be removed for the sake of simplicity, and they would be balanced like any other spellgems in terms of having cooldowns and mana costs that make them quicker or slower to use repeatedly. Gem dust also would be removed, going along with this.
5. If twenty seconds seems too long on average, then a way to offset that would be that if the character stops moving AND takes no damage for a few seconds, then the rate of recharge doubles or something. This is kind of like the "meditation mode" that Toll was talking about. But even just in a normal boss fight, if you're using cover at all there will be occasional 3-4 second stretches (at least) where you're not actively firing spells. Since 20 seconds would be the time to recharge your mana from ZERO to full, 3-4 seconds would be enough to recharge a pretty typical amount of used mana from one volley of attacks against the boss.
Credits for various parts of this idea: Keith LaMothe, Josh Knapp, Toll, Penumbra, Hearteater
Pros:
1. It's simple.
2. It seems to meet all the core goals of making sure that players don't spam their best spells only.
Cons:
1. It takes away any reason to explore for ammo, mana, or what have you. Some might argue this is another pro, but I think that having ammo of various rarities is actually a pretty interesting side diversion. There would always be other things that could be searched for, sure, and perhaps this is such a central thing (nobody can go much of anywhere without ammo) that it would just be a time tax to collect ammo, anyway, rather than a fun diversion.
2. When players use higher-tier spells, they're doing more damage at a cost of more mana-regen time. That takes some of the visceral fun out of having that higher-tier spell in the first place, doesn't it? A possible solution would be to make mana costs of spells not adjust by tier, up or down.
MANA-LESS COMBOS DIFFERENCES FROM CURRENT DESIGN
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1. Mana potions and mana scrolls are completely removed from the game, as is any concept of mana. Spell scrolls would once again become spellgems, as in the previous design, as would gem dust.
2. Spell power would be regulated entirely by their cooldowns.
3. In place of the current mana indicator on the HUD, there would be three different elemental icons that represent the last three spell elements that you've used. Each spell has one and only one element associated with it.
4. The order of the three elemental icons wouldn't matter, but how many match the element of your current spell would have a big effect:
4.a. If zero of the icons match your spell, there's no effect.
4.b. If one of the icons match your spell, your spell gets something like a 10% bonus, but also a 5% increase to cooldown time.
4.c. If two of the icons match your spell, your spell gets something like a 40% bonus, but also a 20% increase to cooldown time.
4.d. If all three of the icons match your spell, your spell gets something like a 40% bonus, but also a 100% increase to cooldown time, and all the icons in the bar get cleared.
4.e. If all three of the icons are different, but one of them matches the spell, then you get a 50% bonus to the spell and 0% extra increase to cooldown time on it.
5. Thus you're encouraged to do two or three hits with one element before switching to another one, or to do chains of three elements with a "finisher" that is matching one of the three in the chain. But it's not a hugely complex system, or something that new players would neccessarily have to understand instantly.
Credits for the bulk of this idea: TNSe
Pros:
1. It's definitely simple in terms of mana, and the combos stuff isn't that complex either.
2. It definitely encourages players not to spam a single spell repeatedly, and even encourages them to mix up colors in a way that is currently lacking from the game.
Cons:
1. As with the first one, there's no ammo or mana restoration to explore for. And all the attendant notes of that.
MANA-AS-AMMO DIFFERENCES FROM CURRENT DESIGN
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1. Mana potions and mana scrolls are completely removed from the game, as is any concept of mana. Spell scrolls would once again become spellgems, as in the previous design, as would gem dust.
2. Basic spells (fireball, fire touch, etc) would be regulated entirely by their cooldowns.
3. Slightly fancier spells (launch meteor, insect orb, etc) would have "ammo" of various sorts. In-game we'd say Charges or something similar.
4. There would be a number of different types of ammo, corresponding to various different kinds of spell functions. So you've got things like short-ranged, long-ranged, mega-damage, and so on, all as individual ammo types. All of those would have appropriate thematic names in the game itself.
5. Any spells that have ammo attached to them would show the little count of how many more ammo they have right on their icon, much like scrolls currently do. So there would be no need for any sort of replacement for the current mana bar.
6. There would be a new "ammo inventory" hotkey and menu option, letting you see the counts of ammo you have even if you don't have any spells that use a given type currently.
7. Most ammo would not be craftable, although some of the really basic types might be craftable at the outfitter. Mostly ammo would be found scattered about inside buildings in place of what is currently dust or mana potions, and in larger quantities in stashes as currently things like spell scrolls and mana potions are. Some ammo types could be pleasingly rare, while most would be reasonably common.
8. Each ammo type would definitely have a finite cap above which you could not collect more of it.
Credits for the bulk of this idea: Baleyg
Pros:
1. It's pretty simple, and it's really familiar to anyone who's ever played an FPS game.
2. It lets us do really amazingly-overpowered rare spells if we so desire, as long as their ammo is incredibly rare and their ammo cap is really low. That's a lot of flexibility, really.
3. It gives players yet another thing to find in stash rooms.
Cons:
1. It gives players another thing that they HAVE to go find in stash rooms, since "having ammo" isn't really an option.
2. It only very mildly encourages players not to spam spells.
HYBRID MANA RECHARGE AND MANA-AS-AMMO DIFFERENCES FROM CURRENT DESIGN
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1. All the design notes from the original "Mana Recharge" idea at the top of the list would apply.
2. The design notes for the "Mana-As-Ammo" idea directly above would apply ONLY for spells that are pretty specially powerful. So all your midlevel and low-level spells would just use the mana-as-heat/recharge concept, but those that are really extra powerful would also need some ammo you'd have to collect.
Credits for this idea: Professor Paul1290 and goodgimp (and the others listed on the other two ideas this is hybridizing, of course)
Pros:
1. It lets us do super-weapons in a way that can actually be balanced, while making the normal spells extremely straightforward to use.
2. It's easy to grasp, and the super-weapons won't show up until the player is already well versed in the basic "mana recharge" functionality anyway, so that really makes it very easy for new players to learn while retaining some later depth.
Cons:
1. It really doesn't encourage players not to just spam the same spell, but if the combo system were added in that would solve that. At the risk of adding some complexity, but probably not in too bad a way. The combo system could even be level gated to level 3 or something, to give players a chance to even build up multiple colors of spells.
ELEMENTAL HEAT/COOLDOWN DIFFERENCES FROM CURRENT DESIGN
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1. Mana, spell scrolls, dust, and all that are completely removed.
2. The current concept of offensive spell cooldowns are already broken out by color; however, these would be changed to instead be broken out by the general class of the spell -- mega-damage, close, range, or whatever.
3. In place of the elemental cooldowns, we'd now have elemental "heat" (really need a better word for that since it has fire connotations). Each time you use a spell of a given color (offensive or otherwise), you'll increase the heat value of its color. There would either be six little meters for that on the HUD (ugh), or little colored heat meters that would show up on each spell matching the color in question on your ability bar (still a little busy visually, but not too horrible).
4. Using an offensive spell of one element would remove half of its heat value in its opposite element, making it so that using opposite spells in tandem is a particularly great way to max your DPS. In other words, a red spell that adds 10 units of heat to red would remove up to 5 units of blue heat if blue currently has any heat. This makes for a sort of implicit combo system for spells.
5. Better yet, the amount of opposing-color-heat-reduction for a given spell could vary. So some might be lower-damage on their own, but reduce opposing heat more efficiently, making them better as a combo than alone.
Credits for various parts of this idea: Penumbra, Professor Paul1290
Pros:
1. It's reasonably simple, although it's pushing the bounds of complexity a bit for new players in particular.
2. In terms of combo systems, it's a pretty straightforward one.
3. All the usual stuff about not collecting ammo, whether you think that's a pro or a con.
Cons:
1. It's really hard to represent graphically in a pleasing and clear way, which is not just a cosmetic worry but also something that would potentially harm new player first-understanding and experienced player understanding-the-current-state-at-a-glance.
OTHER VARIATIONS
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There are some other permutations of the above that could be implemented, of course, and there were some other things that could be done, too.
superking and Olreich had some interesting thoughts about making it so that if you exceed your heat threshold it's not that you can't cast your spells anymore, but instead you take penalties to yourself (presumably damage, plus some sort of elemental effect like slowing cold or catching on fire, perhaps). That would be an interesting twist on any of the heat/recharge related ideas, so it's not really something that would be a core decision choice between any of the given core models.