Here is the full list of all 56 Welcome to Princeland achievements.
4 players inside a vehicle
First fly with Seat Copter
Take down a cargo plane
Enter to Quarantine
Reached Rank 50
Reached Rank 45
Reached Rank 40
Reached Rank 35
Master your Revolver skills
Master your Hunter mastery.
Master your Grenade Launcher skills
Master your Two Barrel Shotgun skills
Master your Mine skills
Master your Magnum skills
Master your Ronan Sniper skills
Master your radiobomb skills.
Master your Rocket Launcher skills
Master your M4 skills.
Master your Railgun skills
Master your Commando Scar skills
Master your Rifle skills
Master your Grenade pistol skills.
Master your AS25 skills.
Master your Flame Thrower skills
Master your Dynamite skills
Master your Spear skills
Master your Desert Eagle skills
Master your Tommygun skills
Master your Suicide Bomb skills
Master your Aug skills
Master your Grenade skills
Master your Baseballbat skills
Master your Hunting Rifle skills
Master your Knife skills
Master your Molotov skills
Master your Handgun skills
Reached Rank 30
Deliver a truck
Master your axe skills
Master your Rusty Revolver skills
Master your Domdom skills
Find & Open a Treasure Chest
Gear up & explode a suicide bomb
Reached Rank 25
Master your Barracuda skills
Reached Rank 20
Master your SMAuto skills
Kill the Prince
Reached Rank 15
Reached Rank 10
Hunt an enemy with Ronan Sniper
Open a hatch
Reached Rank 5
First time on the driver seat
Reached Rank 2