Here is the full list of all 31 Square Heroes achievements.
Earn all other Achievements
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Kill opponent with Nuke Bag
Complete 100 games
Replenish 150% Team ammo
Win DM using only Explosives (3+ players)
Kill with Laser and Machine in round
Kill with Fire! (Flamethrower and Molotov)
Kill with Proximity Mine
Host 20 Internet games with remote players
Host an Internet game with remote players
Capture Gnome opponent almost captured
Re-gen 200% Team health
Kill with Cross-bow and Harpoon
Score three Kill Streaks in a match
Win 5 games in a row
Complete 5 LAN games
Survive Survival!
Win team game 4+ players with 75% or more of team score
Capture 15 Gnomes
Score two Kill Streaks in a match
Score Devastation
Score Mega Kill
Score Multi Kill
Win without anyone else scoring (3+ players)
Play entire round without dying (3+ players)
Re-gen your health twice over
Score a Kill Streak
Score Double Kill
Score First Kill
Complete Tutorial