Krygin, Tyrannical King

Citizens and creatures with 0 power you control
are serfs in addition to their other types.
You may attach an unattached serf to a land you
control any time you could cast an instant.
(You can't unattach serfs without other means.)
If a land with a serf attached would be tapped for
mana, the land produces one additional mana
of a color the land can produce.
If you control at least 8 serfs, unattach all serfs,
put 2 +1/+1 counters on all serfs, and sacrifice
Krygin.