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
Spawn 100,000 bloons during your battles
Win 100 quick play battles on assault mode
Beat an opponent by using a random loadout
Unlock tier 4 upgrades for all towers
Get 3 or more decals
Unlock tier 3 upgrades for all towers
Pop 1,000,000 bloons during your battles
Use tower boost and/or bloon boost 100 times
Reach 125 battle score
Win a battle using bloons with decals
Win 5 quick play battles in a row
Beat an opponent with a lower battle score
Win your first battle
Beat an opponent with a higher battle score