improvises

/IH1 M P R AH0 V AY0 Z AH0 Z/
verb
  1. 1

    To make something up or invent it as one goes on; to proceed guided only by imagination, instinct, and guesswork rather than by a careful plan.

    He had no speech prepared, so he improvised.

Source: https://en.wiktionary.org/wiki/improvise, https://en.wiktionary.org/wiki/improvises