Here is the full list of all 20 Emily is Away achievements. It takes around 0-1 hour to unlock all of the achievements on Windows.
Complete Chapter 5
Complete Chapter 4
Complete Chapter 3
Complete Chapter 2
Complete Chapter 1
Use the Undertale Icon
Use the John Cena Icon
Use the Clippy Icon
Use the Portal Icon
Use the Nyan Cat Icon
Use the Sigur Ros Icon
Use the Dota Icon
Use the Isaac Icon
Use the Kappa Icon
Use the Doge Icon
Use the Fallout Icon
Use the Zelda Icon
Use the Stanley Parable Icon
Use the Half-Life Icon
Use the Elegy for a Dead World Icon