red slimes in story mode

[『Johan』]

yo where are them i'm missing their card

[Snaz]

I forgot :(

Orange = desert
Green = wilderness
Blue = winter
Red = Arena? I am not sure if that is where to get card though

[Snaz]

Red Slimes are variant of slimes, that leave red goo wherever they jump. Walking on their goo is slower than on clear ground. They appear only in Arcade Mode or summoned by Furious Gigaslime.

I think you get it from the arena fight -- you can start the arena fight in the collector academy if you go upstairs and go to the left side across from the research room

[Marioalexsan]

Not exactly. Since the Frontline update, you can cause Red Slimes to spawn around Evergrind Fields once you complete a certain quest in Marino's Mansion (Defeating Furious Giga Slime in the quest "One Measly Slime", to be more specific).