Arissa's Echoing Fury

You whisper an arcane phrase, and two shimmering silvery echos of your weapon form trailing it as it moves. For the duration of the spell whenever you make a successful  melee weapon attack you deal an extra 1d8 force damage to the target for each echo.

At Higher Levels.  When you cast this spell using a spell slot of 2nd level or higher, another echo forms, and the damage increases by 1d8 for each slot level above 1st.