Why do the characters in Final Fantasy IX turn pink when they Trance? It’s because their Limit Break is a homage to Final Fantasy VI.
Terra’s Trance is enabled when she rejoins the party in Zozo. While Terra is transformed, the damage she deals is doubled and the magic damage she takes is halved. Her ATB gauge is replaced with a green gauge that slowly decreases, and when it empties she turns back into a human. The length of time Terra can stay in Trance depends on the amount of Magic AP she has gained after battle. If she has not gained enough, she cannot enter Trance, and if her Trance gauge depletes during battle she will not be able to enter Trance in the next battle until she acquires enough Magic AP again. The maximum amount she can have is 255. Terra can also change back into a human at will with the Revert command.
We’re able to unlock Terra’s trance in the story:
Terra’s Strength, Stamina, Speed and Magic Power double. The length of time Terra remains transformed depends on her Magic Points―the more she has, the longer she stays Tranced. Trance can be used once per battle, unless Terra is killed while Tranced or uses the Revert command to cancel Trance before it expires.
All characters in Final Fantasy VI have a trademark ability, but Trance is Terra’s.
In Final Fantasy IX, it isn’t explained why all characters are able to Trance, they just do when their emotions are heightened in battle.
Trance is a surge of powerful emotions that momentarily enhances one’s inner capabilities, and thus the effects are unique to each individual.
Otherwise, from a narrative perspective, it makes perfect sense for Zidane to have Trance as his Limit Break. Zidane is a Genome from the planet Terra, designed as a war machine. So then his Limit Break is actually a part of his character.
Maybe the fact that Terra is inside of Gaia is how the characters are able to get extra powers?
There’s one other way in which Final Fantasy IX as a homage to Final Fantasy VI. That’s the inconvenience of using them:
When a character is in Critical status, there is a 1 in 16 chance they will perform a Desperation Attack upon the Attack command. Characters will never use their Desperation Attacks during the first 25.6 seconds of battle.
In this sense, you can’t control them because they activate randomly “after using the Attack command when at critical health”. In Final Fantasy VI and IX, the battle might end before you Trance. Or, Trance might leave the character on your next turn. Only in Final Fantasy IX, you don’t need to be in critical health to use a Trance. But in both cases, Trance is fleeting and hard to control. The strategy may come in hand for some players, but it’s just random luck.