According to an article in the 15 February 1997 issue of V-Jump, the cactuar was designed by Tetsuya Nomura based on a doodle he drew on a notebook when he was a high school student. They bear a resemblance to Japanese "Haniwa", a type of clay figure made for ritual and funerary uses.
Cactuars are usually very fast, and tough to hit. Their HP is usually low, but their defenses are high and they often yield large amounts of gil and EXP. Often, they counter most attacks with 1000 Needles (Blow Fish in some versions of Final Fantasy V and Final Fantasy VI), which always deals 1000 HP of unblockable damage that ignores Defense. Usually, this ability can be learned as Blue Magic.
In some games, such as Final Fantasy IX, cactuars may be underground and will only counterattack if they are hiding. Some games have stronger versions of this attack, such as the 10,000 Needles. Cactuars are often weak to Water.
The Gigantuar, also known as the Jumbo Cactuar, is a recurring boss type of cactuar. They are bigger versions of the cactuar and sometimes sport a mustache. In some occurrences, Gigantuar has the attack "10000 Needles", with an additional "99999 Needles" in games where the max HP limit is more than 9999.
Good luck cactus-chan! I made sure to sage with my message to wish you luck.
"Choose all pictures with a cactus" Just happened twice.