Cylinders are always vertical. From the PHB chapter on spells:

The circle must either be on the ground or at the height of the spell effect. [...] The spell's effect then shoots up from the base or down from the top, to a distance equal to the height of the cylinder.

they forgot to add tempest domain

Quote from yogg_saron >>

suprised noone has mentiond this yet but one of the great things of this spell in the flamestrike vs fireball ... fireball requires you to be able to see your target And have a direct line of sight
this? this i can just cast saying that house thats 40ft behind me? i want it about 10ft in there where i know that person is. (you can describe your target location like with dimension door, unlike with fireball)

 Fireball doesn't say anything about needing to see the target either. However all spells require a clear path from the caster to the target (ref). Both Fireball and Flamestrike can hit enemies that are invisible or obscured by fog or darkness, but not ones that are behind a wall (assuming the wall fully encloses the target or is long and tall enough to prevent indirect targeting).

However, one case where a cylinder can be better than a sphere is if an enemy is behind a long, 30-foot tall wall with no roof. With Flamestrike, you can target a point in the air 40 feet above the enemy's head and direct the cylinder downward.

why do fiend warlocks get this when they already get fireball?

So on a successful save, does the creature resist all the damage or just the radiant? 

Thinking of ways to fix this spell. I thought of making the column of the strike last until the start of your next turn, or for two turns in total.

To give it the feel of some firey wrath coming from above, that can cause extra damage from a burst/culmination effect when it switches off...

Would feel and look epic, without a huge increase in damage(as creatures would have just moved out of the way if they could), but might just give it a niche.

Quote from yogg_saron >>

suprised noone has mentiond this yet but one of the great things of this spell in the flamestrike vs fireball ... fireball requires you to be able to see your target And have a direct line of sight
this? this i can just cast saying that house thats 40ft behind me? i want it about 10ft in there where i know that person is. (you can describe your target location like with dimension door, unlike with fireball)
simpel combat example, (maybe niche but whatever) enemy casts wall of force you fireball it explodes on the wall even if you target behind it .. you flamestrike behind it and fk his concentration 

 You can target a fireball through a wall of force, as the wall is transparent.  Wall of stone is the way to block spellcasters.  

Quote from EnchantedNinja12345 >>

Quote from yogg_saron >>

suprised noone has mentiond this yet but one of the great things of this spell in the flamestrike vs fireball ... fireball requires you to be able to see your target And have a direct line of sight
this? this i can just cast saying that house thats 40ft behind me? i want it about 10ft in there where i know that person is. (you can describe your target location like with dimension door, unlike with fireball)
simpel combat example, (maybe niche but whatever) enemy casts wall of force you fireball it explodes on the wall even if you target behind it .. you flamestrike behind it and fk his concentration 

 You can target a fireball through a wall of force, as the wall is transparent.  Wall of stone is the way to block spellcasters.  

 I've always ruled that Fireball doesn't pass through a WoF since Fireball's text says (paraphrasing) "A beam of light streaks from your fingertip to a point you can see within range" , which I think the wall would interrupt the progress of. But there's a whole other debate on that spell because it's so poorly worded. 

 You can target a fireball through a wall of force, as the wall is transparent.  Wall of stone is the way to block spellcasters.  

False, it has been confirmed that anything behind Wall of Force has total cover, and so most spells can't target anything behind it. Especially not Fireball, as it includes a projectile in the form of a "bright streak", which the wall will block.

So rude that Druids can't take this spell anymore

Id rather cast guiding bolt at level 5. No save and 9d6 radiant damage. Its only one target but 10ft your usually only hitting 2 anyways. 

Interesting 

"A vertical column of divine fire roars down from the heavens..."
Does this work indoors, our under overhangs?
The spell description specifically specifies "the heavens", insinuating that it is a sort of "piercing the clouds" type of deal.
Does it work similarly to "Call Lightning" needing a big space to work, or is it just flavor?

I think since it is the heavens it will hit no matter what, but if you DM you could say it doesn't work if there is cover.

Honestly to make this a little bit better give it the same mechanic other cleric damage spells have which is allowing you to pick targets and damage type (necrotic or radiant). It would put it in line with the spells spirit guardians and destructive wave and if the idea behind this spell being weaker is for the cleric spell list to be thematic then it really should have consistent themes like that.

It would still probably under perform and could probably use a 15ft area and a rider like allot of cleric spells have. Maybe being a healing stopper given that it kind of already does that with the combo of fire and radiant. May as well make it consistent. 

This lets you just smite some goblins and have them think you’re god.

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