Failed Experiment is a specimen that inhabits the Shinra underground facility. Prior to its transformation, it lived as a human. Due to the intervention of transplants, the human transformed into an abomination. Failed Experiment is weak to ice.
Defeat all surrounding enemies.
Before you encounter Failed Experiment, you need to get rid of the Unknown Entity on the platform. Have Tifa take out all the enemies on the platform to complete the first half.
Use Group Abilities.
Ice materia fares well against the Failed Experiment. When the fight starts, you’ll need to take out the horde of Unknown Entities. Combine regular attacks with group abilities such as Starshower and Maximum Fury to whittle them down.
Focus on the boss’ Appendages.
When the boss appears, shift your aim towards it and attack its appendages. If you’re using Tifa and find that she’s having trouble against the wave, swap to Barret and have him focus on the limbs.
Use Ice spells or summon Shiva.
After breaking the appendages, you’ll expose its heart. You can opt to summon Shiva, otherwise bombard him with attacks like Blizzaga.
Use Barret and support from the back.
Eventually the boss will toss the surrounding enemies. Barret isn’t the best at dodging attacks but with Tifa, she should keep the boss busy from relying on much of the ranged attacks. Continue to support Tifa from the back by attacking the appendages and then blasting the heart