With the Add-On Pack you get access to 28 cards: 24 additional creature cards (12 new creatures with duplicates) and 4 additional Mindbugs (required to play the 4-player mode).

List of creature cards:
Bugserker (x2)
Count Draculeech (x2)
Creep from the deep (x2)
Ferret Pacifier (x2)
Froblin Instigator (x2)
Goreagle Alpha (x2)
Hamster Lion (x2)
Hungry Hungry Hamster (x2)
Hyenix (x2)
Majestic Manticore (x2)
The Lurker (x2)
Turf the Surfer (x2)
The Kickstarter version of this expansion also included the following promos. These promos are also available in Mindbug: First Contact – Promo Pack 2022.

Slugapult (P1/2021)
Mindbug Bug (P2/2021)
Ratomancer (P3/2021)
Ram Hopper (P4/2021)
Boar-Zooka (P5/2021)
Sluggernaut (P6/2021)