Astro, Lone "Wolf"

Devour 1 (As this creature comes into play, you may sacrifice any number of creatures. This creature comes
into play with that many +1/+1 counters on it.)
If you control no other creatures, then Astro,
Lone "Wolf" has haste, trample, and menace.
{5}{g}{g}{g}, sacrifice 3 creatures: return Astro,
Lone "Wolf" from your graveyard to the battlefield. Activate this ability only during your
upkeep.