Ability Efficiency linearly affects the energy cost of Warframe abilities. All Warframes have a base Ability Efficiency of 100%; Ability Efficiency over 100% indicates a reduction of ability cost while Ability Efficiency below 100% indicates an increase in ability cost. The Arsenal will not display an Ability Efficiency above 175% because abilities cannot consume less than 25% of their base costs.
Channeled abilities drain energy at a specified rate. Ability Efficiency affects the energy drained at each tick as expected, but because Ability Duration affects the amount of time between these ticks, the formula for effective Ability Efficiency for channeled abilities is as follows:
An important point worth mentioning is, as seen in the spreadsheet on the right, that the cost of such abilities is minimized at 190% efficiency and 40% duration, which is achievable with just two mods (Streamline and Fleeting Expertise). (The game displays 175% efficiency, but in actuality, the real formula is the sum of all mods.)
The in-game energy bar display is rounded down to the nearest whole number, but the costs of the abilities are not. This results in the discrepancies in the apparent cost of abilities with Ability Efficiency mods. For example, an ability with 25 energy base cost will cost 17.5 energy with maxed Streamline (+30%). If this ability is used multiple times in a row, it will appear to cost 18 energy, then 17 energy, then 18 energy, then 17 energy and so on.
Energy Drain for Toggled AbilitiesEdit
Some abilities are toggled on and last until the user turns them off or runs out of energy, such as Ember's World On Fire or Chroma's Spectral Scream. Energy drain for these toggled abilities depends on both Ability Efficiency as well as Ability Duration. See the related section for a full explanation.
Streamline, Fleeting Expertise, Blind Rage and the positive Ability Efficiency Arcane Helmets stack additively. Stacking with Meridian Trinity Helmet or Scorpion Ash Helmet does not appear to follow this formula; this suggests stacking is different when you have a helmet that reduces Ability Efficiency.
Arcane Helmets also reduce (or increase) ability costs linearly based on the percentage shown on the mod card. The following helmets affect Ability Efficiency:
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