You have made a deeper pact with Ifrit (The Genie). This Djinni has empowered you and your familiar. You can now summon a Flame Mephit with the find familiar spell. This mephit will also improve over time. 
You also gain the Produce Flame  spell added to your spell list. This doesn't count against your number of cantrips known. If they don't appear on the warlock spell list, they are nonetheless warlock spells for you.

At 5th level your summoned Magma Mephit improves. He can now cast any cantrip you can also cast.  It also gains: When your familiar casts a cantrip, your familiar can deliver the spell as if it you had cast the spell.  If the spell requires an damage roll, you use your level of damage modifier for the roll.

At 9th level your summoned Magma Mephit can learn to use magical items. He is only allowed to be attuned to 1 item at a time.