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