Tsuna

When Tsuna enters the battlefield, it explores.
(Reveal the top card of your library. Put that
card into your hand if it's a land. Otherwise, put
a +1/+1 counter on this creature, then put the
card back or put it into your graveyard.)
{1}{u}: Regenerate Tsuna.
Whenever Tsuna attacks, create a 5/5 blue
leviathan creature token with islandwalk into
the battlefield, tapped and attacking. Exile it
during your end phase.