"Terra Firma" is Portuguese for "Firm/Solid Ground".
"Terra Firma" is a Latin phrase meaning "solid earth"
This card is very similar to "Elemental HERO Neos" in ATK and DEF, appearance, and their ability to use other monsters to become stronger. Also, they represent almost opposite things to humans, "Terra Firma" representing Earth, and "Neos" representing Space.
It has a similar design and coloration to "Core", as well as the same Attribute and Type. It is also 1 Level greater than its original form, and has 200 more ATK and DEF. Also, since this card's name refers to the planet Earth, "Core's" name refers to the solid metal center of Earth called its Inner core.
This card is the first "Planet" monster to appear in the manga.
This is the only "Planet" card to not have its name exclusively in English alphabet characters and punctuation.
This is the only "Planet" card to have its name deviate from the standard naming pattern (in the OCG: "The (word) Planet's name in all caps", whereas the TCG equivalent is simply: "(same word as the OCG) Planet's name") following that pattern, this card would be named "The E-HERO EARTH" in the OCG and "Elemental HERO Earth" in the TCG.
This is the only "Planet" card to be a Fusion Monster, whereas the others are Effect Monsters. Also, this is the only "Planet" card that belongs to another archetype besides "Planet" series.
This monster also has an uncanny resemblance to Frieza from Dragon Ball Z, specifically his 4th form when at 100% power, appearing near identical. This is further referenced by his artwork which implies he conquered Earth, similar to Frieza's goals to overthrow the universe.
This monster's color scheme bears resemblance with the Duel Academy Duel Disk.
This is the signature card to Jaden Yuki in the manga.