Here is the full list of all 20 Doodle Tanks achievements.
Maus created
Unlocked all elements of Germany
Unlocked the PaK 44 L/55 and KwK 44 L/38 guns
Bölter created
Unlocked all Germany events
Unlocked Panther, Tiger I, Tiger II
All medium tanks created
All USSR elements unlocked
All TDs created
Unlocked the Pz III and Pz IV tanks
T-34, KV-2, IS-4 tanks unlocked
All inventions created
All light tanks created
All T-34 unlocked
All Lend-Lease supplied tanks unlocked
50 elements unlocked
T-34 unlocked
First tank created
8 groups created
25 elements unlocked