
You don't lose unspent green mana as steps and phases end.
Omnath gets +1/+1 for each unspent green mana you have.
Omnath, Locus of Mana has 7 printings, first in Worldwake (2010). EDHREC ranks it #3,735 among Commander cards. It appears most in Yurlok of Scorch Thrash decks (6,687 on EDHREC). It has 3 official rulings.
Deck counts from EDHREC.
Cards that show up in the same decks on EDHREC.