Here is the full list of all 23 Undefeated achievements.
Giftly Shrine Visited
10,000 gold found
5 sidequests
Beriberu Found
13 secret rooms
Cracilia Slain
Sporarum Slain
1,000 gold found
3 secret rooms
Kingly Lizard Slain
1 hour played
100,000 gold found
Mutant Raflesia Slain
Genu-Geko Slain
Spoiled Rocks Slain
Treesore Slain
Genesore Slain
Lurker Slain
Magasz Found
20 hours played
Finished in less than 6 hours
All 16 sidequests
All 25 secret rooms