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Melee Prowess: Drop sources, locations, and probabilities
Mobs Dropping Melee Prowess
Melee Prowess can be dropped by most ennemies in Warframe. You should probably consider this as your primary farm source.
Other items:
Melee Assimilation - Melee Guidance - Melee Fortification
Melee Vortex - Melee Animosity - Melee Careen
Melee Assimilation - Melee Guidance - Melee Fortification
Melee Vortex - Melee Animosity - Melee Careen