Omnath, Locus of Mana [Commander Collection: Green] Modern Masters 2017 Tokens It becomes a creature again

It becomes a creature again if it's not attached to a creature

(Damage dealt to you causes you to lose life

change Halfdane's base power and toughness to the power and toughness of target creature other than Halfdane until the end of your next upkeep

In this case

Omnath, Locus of Mana [Commander Collection: Green] Modern Masters 2017 Tokens It becomes a creature againSet: Commander Collection: Green Type: Legendary Creature Elemental Rarity: Mythic Cost: {2}{G} You don't lose unspent green mana as steps and phases end. Omnath, Locus of Mana gets +1 +1 for each unspent green mana you have. From the Roil emerged a ravenous primordial being of pure mana.