To obtain green day throw the following on the ground.
5 diamonds
1 book
64 spider eyes

Once you have the green day book and hold it in your hand.

When you have green day you have 3 ability's..

Mold.
To grow mold look down and shift to summon a cloud of mold.
when you summon mold it will infect everything around it and mold will start to grow on them.

Punch.
To punch hold down shift and shift to stop punching.

Poison punch.
Everything you punch will get a poison effect.

Oasis

To obtain oasis throw the following items on the ground
5 diamonds
1 leather
64 dirt

Once you wear oasis you get jump boost speed night vision and slow falling.

Video link
www.youtube.com/watch?v=FDl0o__4cYE