I got lucky when rolling for stats in my current campaign, rolling an 18 and other things. With this + the Telekinetic feat, I'll be pumping (I think) 17.82 DPR WHILE dodging. Adding 4.55 from Toll the Dead gives us 22.37 DPR. Pretty cool considering it's an AOE spell as well, lasts for 10 minutes, and costs a single spell slot. 

Yes it is a 15 feet  sphere

Its noted by the "C" in the black diamond next to the duration.   

Good spell

No, you only designate people not affected by the spell. Everyone else not on a guest list gets wrecked. So if an Assassin is hiding within the radius, they will have to make a wisdom saving throw at the start of their turn.

1. All valid targets will have to make a wisdom saving throw for half damage upon casting, and then again when they start their turn within the radius. If they are removed from the radius before their, like an ally teleports them out, then they only get hit once... for now...

2. You can still move and attack and everything while concentrating on this spell. All other actions are fine. And the spell will keep doing its thing while you are still up and concentrating on it. The only thing to look out for is trying to cast another Concentration spell, as you can only hold one spell at a time. Also, if you take damage, you will have to make a concentration check based on the damage you take. Usually, it is DC (10 or half the damage, whichever is more) Constitution save. Failure means you drop the spell, and it fades out, no longer in play. If you want it back up, you will have to spend another spell slot and an action. Since it is centered on yourself, it will follow you wherever you go.

3. I am not sure, but they only have half speed within the area of effect. So I would assume that it is like they have to spend 2 feet for every 1 foot off movement. If they spend all their movement, they are stuck just outside the Range.

As for tactics, this spell works great in tight spaces with alot of cannon fodder. You can hold the line as the cannon fodder tries to rush past you. You can also have your allies in the sphere with you taking no damage, so long as you designate them as Friend. So the Enemy will run into the circle, and then be face to face with your allies. Use your friends! Also, this works through Cover.

in 5e concentration isn't mentioned in the spell description, its mentioned under the duration section, in the Players handbook it's written as Concnetration, up to X amount of time. On dndbeyond, it's represented by a C next to the maximum duration.

Quote from drakegaming_twitch >>

That can't be what the C in the black diamond means. I get that C on several of my Paladin spells that are instantaneous. Bless, Divine Favor, Protection from Good & Evil, Thunderous Smite, Shield of Faith...not one says anything about having to concentrate. They are either immediate or 10 min durations. So the C MUST mean something else. 

 in 5e concentration isn't mentioned in the spell description, its mentioned under the duration section, in the Players handbook it's written as Concnetration, up to X amount of time. On dndbeyond, it's represented by a C next to the maximum duration.

I know this was 6 years ago, but I as a person need to know that this comments author now knows every single spell he listed was a concentration spell, or I will never stop thinking about it. 

How would you rule on the damage types dependant on alignment in a campaign that doesn't put a lot of emphasis on alignment?

Quote from Kajetan98 >>

How would you rule on the damage types dependant on alignment in a campaign that doesn't put a lot of emphasis on alignment?

When I'm DMing and I come across things like this where alignment has a mechanical effect, I tend to evaluate the character's alignment based on their recent actions and let that be the alignment that matters. Did you just run into a burning building to save some innocent people? Then you're good (for now). Did you just stab a random innocent person for no reason? Then you're evil (for now).

Or another possible approach: the video game Baldur's Gate 3 does not have an alignment system at all, so in that game, you choose whether this spell will deal radiant or necrotic damage when you cast it. (You end up pretty much always choosing radiant because hardly anything resists it while there's a lot of stuff that resists or is flat out immune to necrotic damage.)

Casting this at 6 lvl basically turns you into a walking fireball. :0

Quote from NerdSoda >>

Can I walk towards an enemy with Spirit Guardians active, putting them into the radius and make them take the damage? 

Quote from NerdSoda >>

Can I walk towards an enemy with Spirit Guardians active, putting them into the radius and make them take the damage?

 That seems pretty straightforward going by the spell description. Also as long as they start their turn there, even if they get out with 10 ft of movement, they still have half speed for the entire turn!

Quote from Shazrand >>

Quote from NerdSoda >>

Can I walk towards an enemy with Spirit Guardians active, putting them into the radius and make them take the damage? 

Quote from NerdSoda >>

Can I walk towards an enemy with Spirit Guardians active, putting them into the radius and make them take the damage?

 That seems pretty straightforward going by the spell description. Also as long as they start their turn there, even if they get out with 10 ft of movement, they still have half speed for the entire turn!

Also worth pointing out that it says creatures take damage when they enter it "for the first time on a turn". That's "a turn", not just "their turn". Meaning it's possible for them to take the damage several times during a round if other people keep pushing them into it and then pulling them out again.

Quote from spartan_dumpster >>

If that's the case, what if another player uses this spell? Do the two of you have to be at least far enough away from each other to not intersect, or an extra 5 ft so enemies can go through the gap? Or can they intersect and will enemies just make one save or have to make a save for each if they're inside that area where they interesect? And what happens if one player's does necrotic damage and the others is radiant?

 I love your profile picture SBR is the best!

Cool

You should be able to add people to the unaffected creatures list as a bonus action each turn or something.

Bless is

Quote from wagnarokkr >>

Quote from Shazrand >>

Quote from NerdSoda >>

Can I walk towards an enemy with Spirit Guardians active, putting them into the radius and make them take the damage? 

Quote from NerdSoda >>

Can I walk towards an enemy with Spirit Guardians active, putting them into the radius and make them take the damage?

 That seems pretty straightforward going by the spell description. Also as long as they start their turn there, even if they get out with 10 ft of movement, they still have half speed for the entire turn!

Also worth pointing out that it says creatures take damage when they enter it "for the first time on a turn". That's "a turn", not just "their turn". Meaning it's possible for them to take the damage several times during a round if other people keep pushing them into it and then pulling them out again.

 No, it does not. Stop spreading misinformation.