The discount affects the chosen copy
Touch of Insanity selects a card currently in hand and makes it free for the combat. It is not limited to the current turn like Liquid Memories. Repeatedly drawing and replaying the discounted copy can provide more value than spending it on a Power that does not normally return to the draw cycle after being played.
The effect does not discount every other copy with the same name. A retrieval effect such as Hologram matters because it can return the actual discounted card once that card is in discard. A card still in the draw pile is not a valid target for the potion until it reaches hand.
Additional cost effects need attention. Players report using Touch of Insanity under Borrowed Time and still seeing a positive cost. Borrowed Time adds an energy surcharge during that turn; a free-card effect is not a safe assumption that every separate surcharge disappears.
Recheck the displayed cost after using the potion, especially with cost-changing relics such as Spiked Gauntlets. Choose a target you can actually use and reuse, and avoid planning lethal around the word free without inspecting the resulting hand.
