Black Dragon Master, Rookie

Dragon Student. The Rookie's bond with its dragon partner (and patron) gives it access to an expanded spell list and a black dragon wyrmling companion. The dragon partner can cast spells as an action in place of the Rookie (using the Rookie's spellcasting modifiers) or take the Bite action from its stat block if commanded using the Rookie's bonus action. Three times per day, when the dragon partner makes a Bite attack, it can deal additional damage of its type or recover health points (its choice) equal to 1d6+6.  It takes the dodge action if not given any commands, and if the Rookie is incapacitated, the dragon partner will take any action it deems necessary.  The Rookie gains a swim speed of 30 ft and can breath water.

Dragon Pact. The Rookie and its dragon partner share spell slots (which are recovered after a short rest), but all spells cast by your dragon partner become damage of its respective type. It can cast eldritch blast as a modified breath weapon (see actions). The Rookie concentrates on any spell cast by it or the dragon partner that require concentration. Whenever the dragon partner casts a warlock spell as its action, it gains 4 temporary hit points. 

Dragon Warrior. The Rookie can use its Charisma instead of Dexterity or Strength for its attack and damage rolls when using one-handed weapons. These weapons are considered a spellcasting focus. When it hits with an attack, it deals an additional 3 acid damage with that weapon. It can also add its Charisma bonus to any Intelligence ability check it makes.

Innate Spellcasting. The dragon partner’s innate spellcasting ability is Charisma (spell save DC 14). It can innately cast the following spells:

3/day- melf's acid arrow

Spellcasting. The Rookie is a 6th-level spellcaster. Its spellcasting ability is Charisma (spell save DC 14, +6 to hit with spell attacks). The Rookie has following warlock spells prepared:

(at will): eldritch blast, booming blade, mage hand, armor of agathys

at 3rd level (2 slots): absorb elements, hex, shield, dragon's breath, flaming sphere, invisibility, counterspell, fireball, lightning bolt 

Acid Breath (Eldritch Blast). The dragon partner exhales acid in a 60-foot line that is 10 feet wide. Each creature in that area must make a DC 14 Dexterity saving throw, taking 11 (2d10) acid damage on a failed save, or half as much damage on a successful one.

Shortsword. Melee Weapon Attack: +6 to hit, reach 5 ft., 1 target. Hit: 7 (1d6 + 3) piercing damage + 3 acid damage.

Acid Breath (Recharge 6). The dragon exhales acid in a 15-­foot line that is 5 feet wide. Each creature in that line must make a DC 11 Dexterity saving throw, taking 22 (5d8) acid damage on a failed save, or half as much damage on a successful one.