Interesting, but I need to make a table to see how much costs for how much damage there are.
Number of Lava Rivers | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 |
to pay ability | 2 | 4 | 6 | 8 | 10 | 12 | 14 | 16 | 18 | 20 |
total damage(after using ability) | 2(6) | 6(12) | 12(20) | 20(30) | 30(42) | 42(56) | 56(72) | 72(90) | 90(11) | 110(132) |
Damage plus | 4 | 6 | 8 | 10 | 12 | 14 | 16 | 18 | 20 | 22 |
Damage cost ratio starts with 2 and is by trend reducing to 1.
Edit: Casting LavaRivers gets quite expensive. But if you play just 1 out of your hand and then wait until you casted 5 or 6 before playing further from your hand you get a much better dmg cost.