Baby, the Ruthless Firebat

You have a +2 bonus to attack and damage rolls made with this magic weapon. 
Baby heats up as you land hits consecutively. When you land three hits without a miss you may cause the bat to ignite into flames for 1 minute. When you do baby gains the following properties and access to Batter up and Grand slam

• This weapon does an additional 2d4 fire damage
• the user gains resistance to fire damage
• Batter up : As an action you can have a fireball appear that you can hit, the fireball acts as a 3rd lvl spell with double range. Spell save 13. You can use this feature once per short or long rest
• Grand slam: when batter up is used you can choose to amp up the fireball in exchange of the bats heat, roll a d4 and add the roll to the spells level and spell save. Once this feature is used, baby can’t gain heat until the next dawn

Proficiency with a Warhammer allows you to add your proficiency bonus to the attack roll for any attack you make with it.

Notes: Bonus: Magic, Damage, Combat, Versatile, Push