Because the developers have recently performed a major overhaul of Penguins Arena the achievements have become DISABLED for regular play because of incompatibilities with Steamworks.

If you want to obtain the achievements you need to click properties on your game, go into the BETAS tab and opt into the "Steam Achievements" beta. This will restore the old build of the game and enable all achievements as usual. Please note that you won't be able to play with anyone using the current build of the game until you opt out and patch back up.

Penguins Arena Sedna's World.

Estimated Achievement Difficulty - 2/10
Offline Achievements - 10/10
Online Achievements - 10/10
Approximate Amount Of Time Required For 100% - 4 Hours.
Number Of Missable Achievements - None.
Difficulty Settings affecting achievements - Yes, lowering the difficulty slider ingame or in the menu will disable earning Achievements completely.
Bugged achievements - None, although not all have proper descriptions.
Broken and Unobtainable Achievements - None.

Any issues, mistakes, spelling errors, grammatical horrors or just simple suggestions please post in the comments and I'll try to improve this guide as soon as possible. :)

One on One
Win 10 duels

Duel Master
Win 50 duels

These are perhaps the most annoying achievements to get in the game because the game does not tell what it means by "duel". This does not mean playing the Duel mapmode as most people would guess but instead it means winning a match with only one Penguin left on your team. Although you will get these kinds of wins from simply playing the game the simplest way to farm them is to play a regular match with 4 teams and suicide any additional Penguins you have before knocking off the last enemy.

Bonus collector
Take 50 bonus

Bonus maniac
Take 200 bonus

Tribe's peon
Take part in 40 fights

Tribe's grunt
Take part in 150 fights

Tribe's soldier
Win 20 fights

Tribe's berserker
Win 100 fights

Mass extinction
Win 5 fights in a row

Strong family
Win a match without losing any team member

These are all the regular achievements that you'll get over time from simply playing the game. Should you be too lazy to grind these or just find the game a little too hard all of these achievements, with the exception of the Bonus Collector and Bonus Maniac, can be gotten by simply starting a regular Teams game and leaving it running for 8-10 hours. The two Bonus achievements can then be aquired rather quickly by simply start a duel game with only two teams and just running around picking up the powerups, ignoring the enemy penguin.