Here is the full list of all 15 Sandbox Showdown achievements.
Kill 100 Orcs.
Stumble for more than 30 seconds in a battle. You may want to rethink your battle plan.
Stumble for more than 5 minutes in all of your battles.
Kill over 100 enemies during your battles.
Kill over 500 enemies in Sandbox Showdown. I'm impressed! Whoa, don't hurt me, Your Majesty!
Roadkill 30 enemies.
".. Boom, boom!" While driving, blew yourself up along with two Enemies.
Kill 250 Undead Zombies. Wait, you're not bitten, are you ... ?
Get Tossed 10 Times by Explosion
Beat up 25 People with your fists only.
Take down a T-Rex.
Slay a Troll.
Unlock a Hero's Ultimate.
Kill 3 Enemies with 1 Explosion.
Stumble for more than 30 feet