As a Magikarp: Ioanin didn't do much as a Magikarp, other than suck and train to become a Gyarados. Some of Ioanin's main successes as a Magikarp include, evolving.
As a Gyarados: Ioanin was spectacular as a Gyarados easily taking on almost all Pokemon from Reflection Cave to Laverre City. Some of Ioanin's main successes as a Gyarados include, defeating Korrina's Hawlucha and surviving Reflection Cave.
Just like all of Jared's other Pokemon in this series, Ioanin eventually died. Ioanin met his fate against Gym Leader Valerie. At the start of the battle, Jared immediately switched Ioanin out for Rathalos, who took care of Valerie's Mawile and Mr. Mime. Then when Valerie had sent out her ace, Sylveon, Jared switched out Rathalos for Ioanin. Ioanin then took a bit of damage from Swift, and then hit the Sylveon with Aqua Tail, which took away nearly half of the Sylveon's health. Valerie's Sylveon followed up with Charm, lowering Ioanin's attack harshly, which Ioanin followed up with Surf, taking about 1/3 of Sylveon's remaining health away. The Sylveon responded with Dazzling Gleam, doing major damage to Ioanin. Jared then had Ioanin use Aqua Tail, but it missed! The Sylveon used Dazzling Gleam again, leaving Ioanin with 2 health. Jared was in a tough situation, because Rathalos only had 14 health left, so he couldn't switch out, he had to leave Ioanin in the battle to die. Ioanin didn't even get one more hit in, because the Sylveon out-sped with Quick Attack and killed him.