Here is the full list of all 21 Intralism achievements.
Create new level in editor
Up your profile to level 10
Complete 10 (different) official maps in normal mode
Win multiplayer match
Complete level in multiplayer
Play multiplayer game with other player
Play 5 maps in relax mode
Recieve your rank
Swich workshop filter in maps list from "trend"
Find authors list
Play multiplayer match with workshop level
Play multiplayer game alone
Find your items
Lose within second after checkpoint and resume from it
Launch Intralism
Collect at least one item of each rarity
Subscribe to any level in workshop