A Strength antifire was a planned combination potion that would have been released alongside other combination potions in the second batch of Prifddinas. It would have been created using the Herblore skill, with a level of 92. It would have combined the effects of the extreme strength and super antifire potions.
In order to make this potion, players would have had to buy the recipe from the Meilyr recipe shop, for 300,000 coins. It would have been made by using an extreme strength (4) on a super antifire (4) with a crystal flask in the player's inventory.