How to unlock the skull skin-less for each class!

• Kayla Jones - Doctor: Get to Mars on Full HP
  
• Pacal Lavorin - Mechanic: Fixing Ikatomi to full on Maintenance
  
• Allison Silva - Specialist: "Reroll the same number 3 times"
  
• Jean Olowe - Captain: "Get Extra Dice on already full dice"
  
• John Park - Psychologist: Reduce stress of 2 crewmembers in Operations
  
• Niki Karam - Commander: Resolve an Even with its ability that would be fixable with normal dice
  
• Yuri Novak - Pilot: Move to Command + allow full-crew no damage movement + land on Mars
  
• Joy Lee - "Technician: Have full Assists on landing"
  
• Sofia Diaz - Cannibal: Eat herself to oblivion
  

Normal Difficulty: Send Skulls to Mars gets Solden Skull
Hard Difficulty: Send Golden Skulls to Mars gets Crystal Skull

Events in quotations are the one I am unsure, let me know if they are right or wrong!