Why use mask?
The mask use to open the door which is unlocked by the devil soul not
by key. So you need the amount of mask to open the sealed door. The
mask will neutralized the soul and unlocked the door.

Too many mask?
There are 3 types of mask in the trial version of the game:
Red Mask : Unlocked the door sealed by souls
Blue Mask : Fill up the limit gauge power
Green Mask : Fill up some health

Combo Attack
To use Dante combo attack, you need to equip with any sword and
handgun. First by holding R1 button, push down the analog button and
press D at the same time, when the devil get hit into the
sky, don’t attack and quickly attack by using handgun by
holding R1 button and press ð button. The easy combo is
running and press the D button, Dante will release his
power. Or, by pressing the X button and hit with attack button.

Open the Door!
Some of the door need a devil mask to open it, you need to collect as
many red mask as you can to open it. Some of them need a key.

Easy Killer
To kill the flying doom, equip with shotgun and get near it. Just
released 2 shots and it will be dead and sometimes gives you 3 red
mask, sometimes 1 blue mask, and sometimes green mask.

Use Limit Power
The character have the limit power which can transform it to a devil
creatures. When the blue words above the health screen full, press
L1,X,R1, and ð to release it.

Any weapon?
In trial version of the game there are only 2 types of weapon
available:
Handgun : Get it from the beginning of the game
Shotgun : Get it by hitting one of the table in the game with
bookshelf there