Issues
There is a giant risk to using one, but the reward doesn’t align correctly. Let’s take using a 5 multi explosion, you only get 1.66x more damage compared to 1x from a regular explosion. Not only this, but increased vulnerability.
Proposals
Base
There are many ways to try and buff these options to become more viable. These are just a couple of methods possible. They are buffing it’s damage output, increasing its size, or decreasing its vulnerability.
Option 1: Damage - High Risk, High Reward
The most basic you can get for how to buff multi explosions. One major thing opponents can do is perfect block the first explosion, then hold block on the rest. If they miss the first perfect block, they can stil block the remaining. There would be a much better reward with still high risk.
Damage Statistics
Duration 1: 1.00x
Duration 2: 0.66x (1.33x total) → 0.725x (1.45x total)
Duration 3: 0.50x (1.50x total) → 0.55x (1.65x total)
Duration 4: 0.40x (1.60x total) → 0.45x (1.80x total)
Duration 5: 0.33x (1.66x total) → 0.44x (2.20x total)
Option 2: Increased Size - Medium Risk, Medium Reward
Depending on the amount, you may get a slightly bigger size. A big issue that could happen is an opponent just escaping out of a multi explosion due to how long it lasts, especially on 5 duration. Giving it a bigger size may help keep them inside during the attack. Damage will still be fairly mediocre and vulnerability would still exist to keep things fair.
Size Statistics
Duration 1: 1.00x
Duration 2: 1.00x → 1.10x
Duration 3: 1.00x → 1.22x
Duration 4: 1.00x → 1.35x
Duration 5: 1.00x → 1.50x
Option 3: Reduced Vulnerability - Low Risk, Low Reward
Your endlag would start right when the first explosion comes out, more similar to how single explosions are like. Damage may also get slightly nerfed as compensation. This would allow multi explosions to have coverage of an area, but less of a reward.
Counterpoints
Q: Wouldn’t this make multi explosions meta?
A: It could, but can always be rebalanced if it becomes too overpowered. It’s also nice to have some diversity in the meta instead of always using a few spells.
Q: Aren’t multi explosions already balanced?
A: Not really, they’re really weak in damage and barely any extra damage compared to a low risk but good reward single explosion. You could argue 2 amount has some viability, but anything above 3 really doesn’t.