Here is the full list of all 16 Bloons TD Battles achievements.
Win 20 sequential quick play battles
Win 100 quick play battles on defensive mode
Win 100 quick play battles on assault mode
Get 3 or more decals
Win a battle using bloons with decals
Use tower boost and/or bloon boost 100 times
Spawn 100,000 bloons during your battles
Unlock tier 4 upgrades for all towers
Unlock tier 3 upgrades for all towers
Beat an opponent by using a random loadout
Pop 1,000,000 bloons during your battles
Reach 125 battle score
Win 5 quick play battles in a row
Beat an opponent with a lower battle score
Beat an opponent with a higher battle score
Win your first battle