Here is the full list of all 35 GigaBash achievements.
Defeat a player by using Post-Death and let the remaining player win
As Woolley, use Snowball to roll up all 3 opponents at the same time
Player level 30
Grab a thrown item or a building
Player level 10
Unlock Kongkrete
Complete 1 Teamplay battle
Perform the finishing blow on 3 opponents in a single match (Free For All)
Finish the tutorial
Play in the Gym for 30 minutes
Complete Gorogong story
Complete Pipijuras story
Complete Woolley Story
Complete Thundertross Story
Finish all Story Mode campaign in Apex Difficulty
Finish all Story Mode campaign in Apocalypse Difficulty
Unlock all Titan Lore & Location Bios
Complete 1 Mayhem mode playthrough (5 points)
Complete all sub-objectives in Story Mode
Win 10 matches using Ultimate as the final blow
Spectate a 4 CPU match
Witness J.Lorenz go through an existential crisis as his life's work turns to waste
As Pipijuras, deflect a projectile and defeat someone with it
As Gorogong, Use Double Punch to break the opponent's shield
As Kongkrete, use its passive ability in all 6 biomes
As Rohanna, let your teammate use your Club to win the match (Teamplay only)
Defeat Skorak with his own shell
Win a match using Gigaman without personally destroying any buildings in Kimura District
As Rawa, use Decimate: Supernova to win a match
Complete 10 teamplay matches as Thundatross and have Gigaman as your teammate
Complete 1 online Free-for-all battle with 4 players
Win 10 match in Online Mode
Defeat a total of 100 Titans in Online Mode
Have 5 win streak in Online Mode
Use Zyva and win against all other Titans in online mode