Omnath, Locus of Rot

Whenever a creature card is put into your
graveyard from your library, you gain 1 life
and create a 1/1 black and green Insect creature
token.
Whenever a land card is put into your graveyard
from your library, you lose 1 life add {b}or{g}.
During each of your turns, you don't lose unspent green and black mana as steps and phases end.