Fleecemane Lion

[An Angry Fatman]

{Fleecemane Lion} gets a +1/+1 counter on it from something else, lets say {Galovny Township}. Does it become Mounstrous?

[Mr_Fahrenheit]

From the rulings:

Monstrous isn't an ability that a creature has. It's just something true about that creature. If the creature stops being a creature or loses its abilities, it will continue to be monstrous.

Which means that whether or not a creature is monstrous is independent of the counters it has. The act of it going monstrous gives it a counter, but giving it a counter doesn't make it go monstrous.

[redwolv]

No, monstrous is a status just like the new renowed from magic origins.

When it's monstrosity cost is paid for, the creature becomes monstrous. Most of the time this means adding X +1/+1 counters to it. And in some cases extra effects(like fleecemains indestructability and hexproof, or {stormbreath dragon}'s damage based on cards in hand.

[redwolv]

From the rulings:

Monstrous isn't an ability that a creature has. It's just something true about that creature. If the creature stops being a creature or loses its abilities, it will continue to be monstrous.

Which means that whether or not a creature is monstrous is independent of the counters it has. The act of it going monstrous gives it a counter, but giving it a counter doesn't make it go monstrous.

Dang, I took to long typing.