Wall of Fire

{r}: Level Up
—Level 7-17: any time an opponent attacks you,
they gain a burn counter for each attacking
creature
—Level 18-29: any time an opponent deals
damage to you or one of you creatures, they gain
a burn counter
—Level 30+: any time a player starts their
upkeep with burn counters, they must sacrifice a
land for every 30 burn counters they have