Tearlaments Merrli

When Tearlaments Merrli enters the battlefield, mill
3.

When Tearlaments Merrli is sent to your graveyard
by a spell or ability, you may pay {1}{b}. If you do,
return this card and target creature(s) from your
hand, field or graveyard to the bottom of your
library in any order, then Fusion X, where X is the number of creatures returned to your library. You
may cast each effect of Tearlaments Merrli only once
per turn.