Kairn, Lim-Dûl's Legacy

Other Skeleton creatures you control get +1/+1.
{2}{b}: Regenerate Kairn.
Whenever a Skeleton creature you control is regenerated or a Skeleton leaves your graveyard
and moves to anywhere except exile, you get an
experience counter.
Activated abilities of Skeleton creatures you
control and in your graveyard cost {1} less to
activate for each experience counter you have.