Shouldn't this spell have the warding tag?

This spell is so good! If you know what kinda creatures there'll be in a dungeon, this spell can clear out enormous areas of the dungeon and save a lot of time and HP.

Unless there are walls and doors between you and the targets. The spell still has to follow the rules for targeting.

Where does it say anything about walls and doors obstructing the use of the spell? You don't choose certain targets, you choose a certain creature type, and then that creature type specifically takes damage when entering the range of the spell. Nothing about you needing to see the creature(s).

To give you some idea of the power: 40,000 sq ft equals juuuust under an acre--or in game terms:

• 100ft x 400ft; 20 x 80 squares in 5 sq ft grid, 10 x 40 squares in 10 sq ft grid
• 125ft x 320ft; 25 x 64 squares in 5 sq ft grid, 13 x 32 squares in 10 sq ft grid
• 150ft x 265ft; 30 x 53 squares in 5 sq ft grid, 15 x 27 squares in 10 sq ft grid
• 175ft x 230ft; 35 x 46 squares in 5 sq ft grid, 18 x 23 squares in 10 sq ft grid
• 200ft x 200ft; 40 x 40 squares in 5 sq ft grid, 20 x 20 squares in 10 sq ft grid
• 225ft x 180ft; 45 x 36 squares in 5 sq ft grid, 23 x 18 squares in 10 sq ft grid
• 250ft x 160ft; 50 x 32 squares in 5 sq ft grid, 25 x 16 squares in 10 sq ft grid

But wait... The spell doesn't say the floor plan must be rectangular. Just 40,000 sq ft of space. So you can discount large walls or other solid areas making the area covered even larger.

Mandatory for every mid-to-high level villain stronghold.

Yeah.
This spell helped to ruin the zombie encounter in Tammeraut's Fate.
Lesson learned: just dispel it. Make a caster NPC on the spot and have them dispel it.

Does the damage only happen once, or will it occur every turn the creature is in the area?

Directly from the spell text: "When a chosen creature enters the spell's area for the first time on a turn or starts its turn there..."

So, it triggers *every* round the creature is within the warded area.

Quote from Wienerbarf >>

Where does it say anything about walls and doors obstructing the use of the spell? You don't choose certain targets, you choose a certain creature type, and then that creature type specifically takes damage when entering the range of the spell. Nothing about you needing to see the creature(s).

Quote from TheProfessor757 >>

Yeah.
This spell helped to ruin the zombie encounter in Tammeraut's Fate.
Lesson learned: just dispel it. Make a caster NPC on the spot and have them dispel it.

 Since one could cast it as a ritual, the PC-caster could just recast ist until it sticks, provoking eather an early rush-encounter outside, or the death of the inhabitants because you didn't counter him/her often enough.
Easier would be: have your NPC cast it 30times about 30days in advance (or even before that) making it permanent, since you can't cast Forbiddance into another Forbiddance. Just cancel the one the NPC absolutely wouldn't use/wouldn't get along with (Celestials for Necromancer f.e.).

Quote from Wienerbarf >>

Where does it say anything about walls and doors obstructing the use of the spell? You don't choose certain targets, you choose a certain creature type, and then that creature type specifically takes damage when entering the range of the spell. Nothing about you needing to see the creature(s).

 To clarify for old comments such as the one quoted (this also applies to the Zombie comments), you don't have to see the creatures for it to affect them. What you do need is to be able to target the ground under them. PHB page 204, under the rules for spellcasting, says: "To target something, you must have a clear path to it, so it can't be behind total cover." Thus, you must have line of sight to any spaces you want affect with this spell while you cast it (and seeing through transparent objects doesn't count).

The only way to have the spell go around corners and into several rooms is to move to each of them during the casting of the spell. 

Given the range of touch on the spell, it can also be interpreted that one must touch each square they with to affect. I am unsure about this ruling, however, and so just left it as a footnote.

Tome of the Warlock with this sounds... interesting as heck. 

Quote from jchunick >>

Quote from Wienerbarf >>

Where does it say anything about walls and doors obstructing the use of the spell? You don't choose certain targets, you choose a certain creature type, and then that creature type specifically takes damage when entering the range of the spell. Nothing about you needing to see the creature(s).

It specifically states:  Choose one or more of the following: celestials, elementals, fey, fiends, and undead. 

That, to me, says you can choose one or all of those creature types. I would imagine that it's there to ensure if you had an elemental or celestial with you - as an obvious example - then you could still cast this spell and exclude those types. As another example, a wizard can cast this spell and exclude elementals so the 12th level druid in the party can still wild shape into an elemental.

 Or make a password if the creatures intended to enter the area are outside the warded area

Quote from Wienerbarf >>

This spell is so good! If you know what kinda creatures there'll be in a dungeon, this spell can clear out enormous areas of the dungeon and save a lot of time and HP.

 Undead? Just set the spell to Radiant damage. BOOM! XP! TREASURE!

DM: Jaw opens in shock.

Quote from BlueBurton4 >>

Quote from Wienerbarf >>

Where does it say anything about walls and doors obstructing the use of the spell? You don't choose certain targets, you choose a certain creature type, and then that creature type specifically takes damage when entering the range of the spell. Nothing about you needing to see the creature(s).

 Given the range of touch on the spell, it can also be interpreted that one must touch each square they with to affect. I am unsure about this ruling, however, and so just left it as a footnote.

 That makes no sense. Fireball doesn't require you to pick out each square in the 20 ft radius. The only thing you need to touch is the point in which the spell is cast on. The effects radiate from that point out to the full area.

Quote from Meterex137 >>

 

 

 

Beyond 20

 

 

 

 

 

Quote from BlueBurton4 >>

Quote from Wienerbarf >>

Where does it say anything about walls and doors obstructing the use of the spell? You don't choose certain targets, you choose a certain creature type, and then that creature type specifically takes damage when entering the range of the spell. Nothing about you needing to see the creature(s).

 Given the range of touch on the spell, it can also be interpreted that one must touch each square they with to affect. I am unsure about this ruling, however, and so just left it as a footnote.

 That makes no sense. Fireball doesn't require you to pick out each square in the 20 ft radius. The only thing you need to touch is the point in which the spell is cast on. The effects radiate from that point out to the full area.

That's not the same thing.

Fireball (1) is NOT a touch-range spell, and (2) defines a sphere area via the word "radius." Since the only thing needed to perfectly detail a sphere is the central point and the radius, you shouldn't NEED to pick out the interior squares.

With Forbiddance, it makes sense that some sort of effort needs to be put into defining the area, since there is no specific shape it needs to be in. Touching the floor squares to define the area, or at least the perimeter of the area, makes sense, and it's what I would rule as a DM.

 I suppose it's a safe presumption that this spell blocks entry via Word of Recall? That seems like a missed opportunity.

I fully agree with this rulling.

How does this spell work with Teleport? Does the casting of Teleport simply fail, does it trigger a False Location response, or what?