One of my players uses this at every opportunity. It's starting to get annoying (I'm a new DM too) where he just burns everything in a combat.

Single target much more suited to fire bolt or another similar spell? Burning hands.

Fighting in a flammable building that you're meant to be clearing out, and has a kidnapped NPC in? Burning hands.

Ran out of slots for lightning bolt (his second favourite)? Burning hands.

Unless I or someone else can suggest a much more useful spell for the situation, he casts burning hands until he runs out of spell slots. Then he uses acid splash as a default cantrip.

I get that everyone has preferred spells and I encourage that, but it does get frustrating...

Quote from NeverGiveTheDMIdeas >>

One of my players uses this at every opportunity. It's starting to get annoying (I'm a new DM too) where he just burns everything in a combat.

Single target much more suited to fire bolt or another similar spell? Burning hands.

Fighting in a flammable building that you're meant to be clearing out, and has a kidnapped NPC in? Burning hands.

Ran out of slots for lightning bolt (his second favourite)? Burning hands.

Unless I or someone else can suggest a much more useful spell for the situation, he casts burning hands until he runs out of spell slots. Then he uses acid splash as a default cantrip.

I get that everyone has preferred spells and I encourage that, but it does get frustrating...

Start adding in encounters with enemies that are resistant or immune to fire. 

Unless they're Light domain Cleric, they will probably have horrible AC (my wizard player has just 13 or 16 with Mage Armour), so since they're 15ft away from enemies and it deals 10.5 points of damage on average, any surviving enemies would be able to kill them relatively easily.

it donsent tell you what dc save it is tho (other from that really helpful)

Quote from DnD_epic_dude >>

it donsent tell you what dc save it is tho (other from that really helpful)

 The DC of the save is 8 + your characters Spellcasting Modifier + your characters Proficiency Bonus. 

For example, for a 5th level character with 18 in their spellcasting stat, the DC would be 8 + 4 (their spellcasting modifier) + 3 (the proficiency bonus at level 5) = 15

This is how your characters spell save DC is calculated.

The plane of fire is a great place to be in. I can have this spell cast on my whole body without even having to consume spell slots!

true 

How do you know what the DC is?

Can someone explain why it says range self?

"Spells that create cones or lines of effect that originate from you also have a range of self, indicating that the origin point of the spell’s effect must be you (see “Areas of Effect” later in the this chapter)." PHB Chapter 10 under Casting a Spell, Range.

Cast it as an lv9 spell. that's 12D6 DAMAGE! An average of 42 DAMAGE!

Agnazzar's scorcher is way more accurate to a kamehameha, imo. I mean, it's literally just a straight beam of fire, and does exactly the same thing as this, just with a higher damage die. Plus, it seems way more deserving of the power, seeing as it's literally more powerful and requires a spell slot above minimum.

A Druid can learn this unbelievable 

My friend has this and so do I, I can't wait to use it

Which dice do you use for this?

Does anyone know?

so, is this modeled as a full cone or is this a single, thin, flat sheet? would an apprentice wizard (let's call him Grum'shar hypothetically) kneeling with fingers spread be able to fire this (between guffaws of victory, hypothetically) over an intellect devourer and a prone human without damaging them (but still crisp the standing swashbuckler, paladin, and barbarian (hypothetically))? asking for a friend.

:)

Sounds cool! This is a move I'll definitely use for my Sorcerer :D

That's precisely why I picked this move. It's the closest I'll get to shooting one.