Borrowed Might Potions
After securing the Mandrake Formation and its accompanying compendium, Eren expressed his gratitude once more to Minerva before proceeding to scrutinize the remaining rewards.
Next on his inventory was a transcendent-grade potion enabling the casting of elemental spells with the powers of an S-Rank entity. This consumable, a one-time-use elixir, granted Eren temporary access to a singular S-Rank spell.
There were three potion bottles of this kind. This means Eren could technically cast three S-Rank elemental spells. There would be side effects but Minerva assured that they wouldn't be permanent or life threatening.