Can I persist (or even just cast) multiple copies of the same spell?

[Frostthehero]

Say I'm a high level cleric. I have a snotload of turning attempts, and I want to turn myself into a killing machine.

As far as I'm aware, by RAW, there's nothing preventing me from using my turning attempts to DMM persist e.g., holy star a few times.

Is this really allowed, or have I somehow missed a rule somewhere which prevents this? Bonuses of the same type of course don't stack (barring circumstance bonuses which arise from different sources), so the AC bonus couldn't be ridden into infinity, but it sure does look like one could be dealing multiple CL/2 d6 beams of fire damage each turn as a free action.

If it is allowed, one could imagine a high-op game wherein a cleric persists even more holy stars (possibly using energy substitution to change the damage type of some or all), and maybe uses metamagic rods of greater maximize to allow himself to dish out hundreds of (admittedly, single target) damage as a free action every turn, or have multiple stacks of spell turning (which I understand do not stack, but he could keep only one active at a time and rotate them out).

Thoughts?

[Darg]

Holy Star's effects aren't bonuses except for the bonus to AC so that won't stack. The way you want to do things is rules legal. The only problem is that the PHB gives the DM free rein to limit your free actions. So the DM is well within their rights to say that it might be a free action, but you can't use more than one of those from the spell specifically on a turn. You'll just have to talk to the DM and see what they are ok with.

[Vaern]

Only one instance of a given spell can be active at once. You can cast the spell on yourself as much as you want, but multiple castings will not provide any additional benefit. The rules for stacking magical effects state, separately from stacking bonuses specifically, that if multiple instances of the same spell are cast then either the most recent instance of that effect takes priority, or the most powerful casting of it's multiple instances of the same effect cast at different strengths.

[Biffoniacus_Furiou]

Range: 0 ft.
"You create a glowing mote of energy that stays near your shoulder..."

Holy Star specifically creates an effect that follows you, you're not casting it on yourself as if it were a personal-range spell. Thus the rules of multiple spells on the same target don't apply here. It's handled in the same way as casting multiple Summon Monster spells and having them follow you.

The only limit to how many you can have active is whatever arbitrary limit on free actions your DM puts in place. You could get enough pearls of power and nightsticks to cast it a hundred times, but if your DM only allows you to activate three on your turn then there's not really any point.

[KingJames]

Only one instance of a spell can affect a creature at once.

[Biffoniacus_Furiou]

Only one instance of a spell can affect a creature at once.

While that's true, it's not applicable in this case. Holy Star is not cast on your character.

Range: 0 ft.
Effect: Protective star of energy

It doesn't have a Target entry, it creates something. You can cast as many of the same spell that creates something as you want, unless the spell itself says otherwise.

[Auerkan]

I would like to note that, far as my understanding goes, new casting of Holy Star would not negate previous ones EVEN IF it was a targeted magical effect. I specifically checked out PHB(starting at page 171), and there is not a single paragraph that seems to me as validating this idea. In fact it is directly stated that outside of special cases, a spell does not affect other spells. Holy Star does not have any dedicated clauses, and does not match any of the clauses specified in PHB.

[Crake]

Only one instance of a spell can affect a creature at once.

Citation needed.

Nothing in the combining magical effects rules state that you cannot have a second casting of a spell on you at any given time:

Combining Magical Effects

Spells or magical effects usually work as described, no matter how many other spells or magical effects happen to be operating in the same area or on the same recipient. Except in special cases, a spell does not affect the way another spell operates. Whenever a spell has a specific effect on other spells, the spell description explains that effect. Several other general rules apply when spells or magical effects operate in the same place:

Stacking Effects
Spells that provide bonuses or penalties on attack rolls, damage rolls, saving throws, and other attributes usually do not stack with themselves. More generally, two bonuses of the same type don’t stack even if they come from different spells (or from effects other than spells; see Bonus Types, above).

Different Bonus Names
The bonuses or penalties from two different spells stack if the modifiers are of different types. A bonus that isn’t named stacks with any bonus.

Same Effect More than Once in Different Strengths
In cases when two or more identical spells are operating in the same area or on the same target, but at different strengths, only the best one applies.

Same Effect with Differing Results
The same spell can sometimes produce varying effects if applied to the same recipient more than once. Usually the last spell in the series trumps the others. None of the previous spells are actually removed or dispelled, but their effects become irrelevant while the final spell in the series lasts.

One Effect Makes Another Irrelevant
Sometimes, one spell can render a later spell irrelevant. Both spells are still active, but one has rendered the other useless in some fashion.

Multiple Mental Control Effects
Sometimes magical effects that establish mental control render each other irrelevant, such as a spell that removes the subjects ability to act. Mental controls that don’t remove the recipient’s ability to act usually do not interfere with each other. If a creature is under the mental control of two or more creatures, it tends to obey each to the best of its ability, and to the extent of the control each effect allows. If the controlled creature receives conflicting orders simultaneously, the competing controllers must make opposed Charisma checks to determine which one the creature obeys.

It does appear that you can fire off as many beams per round as you can persist holy stars, and this isn't exactly a new fantasy trope, characters with floating orbs that follow them that shoot magical beams is not uncommon.

Personally, as a DM though, I would put a limiting clause on it regarding how many you can have out at a time, as it was clearly not designed with the expectation of being persisted in mind, so the designers expected it's short duration and high spell level to be enough of a limiting factor on the spell.

[Maryring]

Eh, as a DM I wouldn't limit it. It's entirely rules legal, and can easily be countered by some basic energy resistance.

For the basic question, spells with a duration only has the best/strongest effect on the target, but Holy Star creates a new target with every casting, so this particular spell is freely stackable.

[Darg]

I guess technically the motes could interfere with each other. If they follow the same rules of how to position themselves near the shoulder, then they would need to occupy the same space.

Think of it like flame blade. What's keeping you from stacking them in one hand and multiplying the damage? The blade is immaterial, so it's not like it takes up space.

Just something to think about as the rules don't actually mention anything like this can't stack.