Marauder

As a Marauder, you have honed your skills from that of a standard warrior to that of a bandit or raider. You use your immense speed and strength to rush down and overpower your enemies. You command flames to destroy your enemies defenses and can weave in and out of the dark of night and the light of flames. Your reasons for choosing this lifestyle of pillaging and burning could be out of necessity, having no money to your name and needing to make ends meet, or you could be part of a nomadic nation where pillaging is part of their culture. 

Overrun and Conquer

Starting at 3rd Level, you have honed your body to overwhelm your enemies with speed and power.
All of your movement speeds above 0 are increased by 5 feet. This speed increases further at 10th Level (10 feet), 15th Level (15 feet), and 18th Level (20 feet).
If you move at least 15 feet in a straight line, the first successful weapon attack you make this turn does additional Fire Damage equal to your Fighter Level.

Scorched Earth

Also at 3rd Level, you know that once a site has been pillaged, you must leave no remains.
You learn the Create Bonfire Cantrip.
You also learn one other Cantrip of your choice. The Cantrip you choose must do Fire Damage.
CON is your spellcasting modifier. The DC of this spell equals (8 + Proficiency Bonus + CON Modifier).
You also gain proficiency in the Sleight of Hand Skill and Thieves Tools.

One With the Flames

At 7th Level, you have learnt how to weave your flames into your offensive flurry.
You become resistant to Fire Damage.
If you land a successful weapon attack on an enemy, opportunity attacks against you from that enemy have disadvantage until the start of your next turn.
You can also choose to use one of the attacks granted by your extra attack feature to cast your Create Bonfire or chosen fire Cantrip.

Harness Flames

At 7th Level, your empowered flames can wreath your weapon in flames to burn away any and all resistance you meet.
When you are within 15 feet of the bonfire you create with your Create Bonfire Cantrip, you can use your Bonus Action to instantly end concentration, wreathing your weapon in its flames. The weapon currently wreathed in the bonfires flames deals both its normal damage, and the Fire Damage of the Create Bonfire Cantrip, with no Dexterity Saving Throw made.
This flame lingers on your weapon for 1 minute before fading.
You are still able to use your Create Bonfire Cantrip while your weapon is wreathed in flame.

You can use this special Bonus Action a number of times equal to your CON modifier. You regain all uses of this feature when you finish a long rest.

Raging Flame

Starting at 10th level, your usage of flaming bonfires lets you burn away enemy defenses.
Your weapons and spells now ignore resistance to Fire Damage.
If an enemy has taken Fire Damage on this turn, all weapon attacks you make against that enemy are considered Critical Hits on a d20 roll of 19-20.
You have advantage on Saves made to avoid or end the Frightened condition.

Snuff the Flames of Hope

At 15th level, your proficiency for spreading flames has led to you finding ways to overcome even the strongest of resistance you face.
Your weapons and spells now treat immunity to Fire Damage as resistance instead. This resistance is not ignored by your Raging Flames feature.
In addition, when you deal extra Fire Damage to an enemy with your Overrun and Conquer feature, you can force the target to make a WIS Saving Throw against your spell save DC (8 + Proficiency Bonus + CON modifier). Should the target fail, they become Frightened of you for the 1 minute. The Frightened creature can repeat the Save at the end of each of its consecutive turns, ending the effect on a success. 

Firestorm

At 18th Level, you have become a master of the great power of flames, as if you were an icon of fire itself.
You learn the Spells Scorching Ray, Heat Metal, Fireball, Flame Arrows, and Wall of Fire. You can cast each of these Spells once before needing to finish a long rest to cast them again.
Each of these spells is cast as if casted from a 6th level spell slot.
CON is your spellcasting modifier for these spells.
The DC of these spells equals (8 + Proficiency Bonus + CON Modifier).