The card works in quite similar means as other "Manland" kind cards. You pay the activation cost, it becomes a 2/2 creature with creature types, and also for the remaining portion of the switch it acts exactly as if it had been a 2/2 colourless Llanowar elves (NOTE: this includes summoning sickness. So long as its only a land you are able to tap it for mana as you could a regular land. If you turn it into a creature straight after playing it however, it features summoning vomiting and you CANNOT tap it for mana).
You effectively play this card by using its attacking abilities within right times, its really a "free animal" at the price (that can easily be an advantage) of making it a creature for 1 mana per turn.
The truth that it begins and reverts to a land helps it be safe from sorcery speed treatment most of the time, the truth that it's all creature kinds makes it extremely potent in some tribal decks (legacy/modern merfolk), plus the undeniable fact that it acts as a land through to the point that you'll require that it is an animal makes your deck alot more stable for casting costly means.
If it dies as an animal, it dies. Observe that spells that state "target non-land permanent" cannot target it, it could be a creature, but its still a land. It generally does not return to being a land if it dies, it goes to the graveyard exactly like other things.
The card is pricey because of it is proven track record, which is a rather powerful exemplory instance of a person land because of its low activation expense and positive tribal communications. Merfolk porches will frequently stimulate this as a 4/4 or 5/5 creature.