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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 Vortex
Melee Fortification - Melee Animosity - Melee Retaliation
Melee Assimilation - Melee Guidance - Melee Vortex
Melee Fortification - Melee Animosity - Melee Retaliation