Here is the full list of all 22 SMYS : Classic achievements.
Eat 1 Yumyum
Eat 10 Yumyums
Eat 25 Yumyums
Eat 50 Yumyums
Eat 100 Yumyums
Fail a Quick Time Event
Destroy 10 blocks at once with a bomb
Crush your teammate with a block
Collect 40 blocks or more during a round
Use 20 bombs
Obtain a bonus from Items Generation
Obtain 2 bonuses from Items Generation
Fortify 20 blocks at once with the Structural Reinforcement bonus
Kill an enemy zglub with a bomb
Win a round with less than 15 blocks on your side
Die from your own bomb
Win a round while under a malus effect
Win a round under 30 seconds
Play a 4 player game
Kill yourself and your teammate at the same time with a block
Grab 10 items in a row without missing using the canon
Complete 5 Quick Time Events during the same round