Here is the full list of all 21 Skeletal Avenger achievements.
Try out every kind of perk.
Complete fifty quests.
Collect 100,000 coins.
Collect 10 perks for a single avenger.
Kill 8 enemies with a single skull throw.
Complete a quest using only dash.
Complete a quest without taking any damage.
Complete a revenge in 150 seconds.
Kill 50 enemies with deflected projectiles.
Find all item types.
Complete a quest without using your weapon.
Kill 8 enemies with a single primary attack hit.
Kill 25 enemies within 10 seconds.
Have 100 enemies killed by environment hazards.
Started New Game Plus.
Kill Sorcerer's Castle boss.
Kill Dark Caverns boss.
Kill Sewer boss.
Find all trinkets.
Kill Dungeon boss.
Complete the tutorial.