Many players have wondered if this would be a positive solution to the poor MTGA economy, but it seems as if that won't ever happen
If the creature is known to have more than four legssay, it's a spiderbut not all its legs are visible, it still has four or more legs
The biggest drawback here is how costly it is to cast Maralen, but as long as you can exile spells with the ETB ability, you go leaps ahead in mana and cards
Then you get to flip it into a land which means you are kind of playing 17 which is super helpful what with all the 5+ CMC cards you are running
On paper the Primeval Titan seems a bit better with the trample, the card advantage and the ability for the game to get very out of hand however you need the support cards for Primeval and you need the right deck
It can be a two-mana bounce spell if you really need it to be