Happy Wars

The following rules apply to medal achievements:
They must be obtained in either Quick Match or Co-op. Special Games count also.
They cannot be obtained in Player Match or Skirmish Mode.
You must finish the game to the end regardless of winning or losing. Disconnecting or quitting will forfeit any earned medals within the match.

Update: The patch released on June 5th 2015 now counts all past medals earned on the Xbox 360 version!

Bronze Cross medals are fairly easy to obtain, although a few are more luck based over skill. Below is a list of requirements;

Spearhead
Claim the first kill of a match.
Self explanatory. Pick your strongest class and rush ahead of everyone else, as most randoms head straight for the first tower.

Invisible
Claim 10 consecutive kills before dying.
The kills must be done within a short timeframe, roughly 10-15 seconds between each kill for it to string the combo.

A Total Hero!
Kill 5 enemies who've killed allies of yours.
Avenge medal with a strict time from the moment your ally is killed. Stick close to your team, and hunt down any close opposition that gets a kill as soon as possible.

Tyrant
Kill enemies with scores lower than you 10 times in a match.
If you're good at the game, this will be one you'll get often. Not much else to say.

Master Healer
Heal allies 30 times in a match.
Cleric. Spam A on allies. Win big!

Emergency Rescue!
Resurrect allies 10 times in a match.
Cleric... again. This can be hit or miss as Resurrect is a randomly chosen skill. Alternatively, you can add the skill to your weapon.

Death Defier
Resurrect allies 20 times in a match.
See above.

Nightmare
10 kills in 1 game without dying or changing character class.
Pretty much NBK but with only 1/3 of the work needed.

Survive!
Longest survival time for a single game.
Only one player will be shown this medal at the end of a game, but as long as you didn't die alongside other players, this one will count in your total at the end... anyway, just don't die, and hope you get lucky.

The Champion
The most kills in a single game.
Self explanatory. Comes naturally if you're an MLG pro or just have a really bad team not doing much of the work.

Immortality
Finish a game without dying.
You can stack this with Survive! if you want, but at least you're more likely to get this one. Watch your health, and always run to an empty spot to recover if needed.

Dedicated Gamer
Over 50 hours of total play time.
Can only be obtained once.

Veteran
100 total wins.
Can only be obtained once.

Elite Soldier
100 total kills.
Can only be obtained once.

Guardsman
Kill 5 enemies near your army's towers.
Can only be obtained once.
This one will come with natural gameplay. If you really need it done, let the enemy head towards a tower and then take them down.

The Swordsmaster Appears
30 total kills as any Warrior type.
Can only be obtained once. Comes with natural gameplay.

The Demon King Manifests
100 total kills as any Mage type.
Can only be obtained once. Comes with natural gameplay.

The Saint
1000 total healings as a Cleric.
Can only be obtained once.

The Ninja
100 total kills by ambushing enemies from behind!
Can only be obtained once.
You'll need to attack towards the opponent's back. You can get this a bit faster by finding two people already in combat, and then sweep in for the ambush kill. Ambush Attack Up buffs will help out a lot.

Nightingale
Successfully use Resurrect 10 times in one game.
Can only be obtained once.
"Wait, really? One time only?" you say, as you flip tables over. Yeah, for whatever reason this doesn't stack. Anyway, use Cleric and hope you get the skill as you level up.

Prospective Hero
Appear on Hero Pop-up 10 times.
Can only be obtained once.
I think we're seeing a pattern here... um, just play the game. Trust me on this, it will come fast.

Iron Man
Guard against enemy attack 50 times.
Can only be obtained once.
Choose Warrior (or Cleric if you really need to). Run to enemy castle. Use shield. Wait for ballista arrows to hit you. ???. Profit.

Changing Class
Change your character class 10 times.
Can only be obtained once.
Self explanatory. Must be done in one game.

Hello, World
Use talk/order commands 50 times or more.
Can only be obtained once.
Earned through natural gameplay. Unless you really hate building for some reason.

Destroyer
Destroy 10 towers.
Can only be obtained once.

The Finisher
Destroy the Big Tower 10 times.
Can only be obtained once.
Earned through natural gameplay. You must be actively tapping down the tower for it to count.

Desert Journey
10 total wins. (Desert or Zodiac stage)
Can only be obtained once.

Marine Expedition
10 total wins. (Coral or Deep Sea stage)
Can only be obtained once.

Fantasy World
10 total wins. (Rainbow or Snowman stage)
Can only be obtained once.

Sent to the Netherworld
10 total wins. (Twilight or Pumpkin stage)
Can only be obtained once.

I Like High Places
10 total wins. (Bird God or Sunset stage)
Can only be obtained once.

Ketchup Lover
10 wins total. ("Ketchup Avenue" stage)
Can only be obtained once.

Formidable Enemy Crusher
Defeat an enemy marked 'Formidable' in a Special Challenge.
I'll have more details on this later.

In Your Face!
Kill the special enemy in a Special Challenge.
I'll have more details on this later.

This one is pretty much achievable by playing quick matches and co-op matches but if it doesn't pop naturally just sit on a turret in the home castle during a co op match and you'll pretty much be guaranteed two bronze crosses for surviving.

You normally get two medals just for sitting there plus one if you get the first kill (just make sure you don't die)

You will also get a good chance at killing the gate-crashed which is an extra broze cross!

This will also be an easy way of getting the Happy War-Lord achievement