When Omnath enters, draw a card. Landfall — Whenever a land you control enters, you gain 4 life if this is the first time this ability has resolved this turn. If it's the second time, add {R}{G}{W}{U}. If it's the third time, Omnath deals 4 damage to each opponent and each planeswalker you don't control.

Landfall — Whenever a land you control enters, create a 5/5 red and green Elemental creature token. Whenever Omnath or another Elemental you control dies, Omnath deals 3 damage to any target.

You don't lose unspent green mana as steps and phases end. Omnath gets +1/+1 for each unspent green mana you have.