Majoru Oakheart said:
Most people refer to nova as just meaning "Using all your best spells at once". Sometimes you nova by using your highest level summoning spell, sometimes it's your highest level damage spell. Basically, it's just a "Why use a fireball when you have a meter swarm available?" question.
Well, using all your best spells at once is what causes the "spike." But if your best spells don't actually spike anything -- if they are long-term effects, rather than one-time effects -- there's no sudden increase in output. Just a modest bump that brings you in line with what the others are doing on a regular basis.
It gets more useful. If a summon spell does 200 damage instead of 50 damage, then you've killed the enemy with less expenditure of resources. Which means the battle was easier and you are more able to handle more, if you have to.
If a summon deals 200 damage over 4 rounds, then a "spike" deals 200 damage at once. The output over a given number of rounds is equal. The fighter is dealing 200 damage over 4 rounds, too. The worry about the nova is usually that they can do that 200 damage that is supposed to be once every 4 rounds, and make it EVERY round, by ending the encounter early and then recharging it. But if the game takes this into account by being capable of having encounters that are a full day in one, then the encounter doesn't end early -- it keeps going.
Maybe an example would help. We'll keep it simple and abstract. Fighter deals 5 points of damage every round. Wizard deals 50 points of damage for their "nova" effect (fireball!), and otherwise can't actually deal any damage -- weak wizarding arms y'know. Monsters have on average 50 hp. In a "normal adventuring day", this party of two fights two monsters: the wizard nukes one, and then the fighter chops away at the other.
The wizard then gets the genius idea for a 15MAD, so that the wizard can kill all the monsters all by herself: kill one monster, rest & recharge, then come back and kill the other.
The party goes out and has the wizard kill one monster, and then take a rest. Only, when they come back, they find that they must fight TWO monsters at once -- the DM has employed the system's ability to cram a whole day's worth of encounters into one encounter, and so the Wizard has lost the ability to exploit resting mechanics to always be at full power. The wizard still kills one monster, and the fighter still kills the other.
The wizard can still ask to rest after that one big fight, but the challenge has remained the same, the fighter still got to kill their monster, and the wizard still ran out of resources, so there's no balance issues. There might be a subtle pacing issue if the DM isn't comfortable with one big cinematic fight per day, but maybe the party will go back to stretching out their day instead, so they can pick off the monsters one at a time again.
So, what if the wizard summons something instead of using a fireball? Well, the wizard has just gained the miraculous ability to deal 5 points of damage every round instead of 50 points of damage at once. The wizard now equals the fighter.
So, what if the fighter employs 4e style daily abilities instead of just swinging their sword? Well, the fighter has just gained the miraculous ability to deal 50 points of damage once per day, instead of 5 points of damage every round. The fighter now equals the wizard.
The thing with summons is that you can summon them and do as much damage as the fighter buddies in addition to the other spells you cast...making you twice as good.
Oh, now the wizard has two spells? One that deals 50 damage, AND one that deals 5 damage per round?
Well, what's the fighter been doing this whole time the wizard has been getting another spell? Clearly, not just sitting at 5 damage per round like he was back when the wizard only knew one spell. Now, he's doing
10 damage per round (perhaps he has multiple attacks now!). Of course, our monsters now have about 100 hp, so it's not like it's much different, all told. The wizard still kills one (half it's HP in one fireball, half of it from the summon), and the fighter still kills one (all of it from attacks). Well, the fractions realistically get a little messy (maybe Fighter and Wizard each kill 1/2 of each monster; whatever), but the principle remains the same: a nova gives no real advantage.
Now, there can still be kind of genre issues with the 15MAD (one big combat feels a lot different than several smaller ones), but there's no longer
gameplay issues with it -- it offers no tactical advantage, so there's no incentive to try to game the system like that.
It would be especially potent if combined with some requirements for rest -- say, resting consumes food, components, and other "upkeep" items. And extra-savvy in combo with adventure design that helps limit it (time limits, dangerous environments, etc.).