Here is the full list of all 40 Viral EX achievements.
Complete Sector D
Complete a stage using only headshots
Kill 3 enemies with a single boom shot
Knock a trap ball into an enemy
Complete Sector C
Get a 'clatter'
Shoot 10 Thor shots
Complete Sector B
Defeat Odin without retrying
Get 5 'long shots' in a stage
Attain your first 3 skull rank
Complete any stage using only rebound shots
Get a rebound on a platform enemy
Get 10 headshots
Complete Sector A
Get a 'splat'
Deflect a shot into an enemy
Shoot a multiplier
Earn a combo
get a 'rebound'
Get 100% accuracy on a stage
Hit an enemy after bouncing off 2 walls
Get a 3 skull rank on every stage
Complete Sector E
Complete Sector F
Complete Sector G
Complete Sector H
Complete Sector I
Complete Sector J
Shoot a firewall 5 times inquick succession
Get 100% accuracy on all 50 stages
Get a long shot over 100 metres
Shoot Odin 20 times whilst invincible
Hit all of Odin's shots
Stop a Thor shot in close proximity
Kill more than 1 target with the multi-shot
Eliminate all enemies in B-1 'I Know a Way'
Get 5 multipliers in 1 stage
Earn a 5 hit combo
Earn every Viral trophy