Look at the description of the skill with the Cost enchantment — it says it reduces MP consumption.

Now, take a look at the skill’s parameter:
<enchant2 levels="30" name="Cost">
<table name="#count">11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40</table>
<table name="#activateRate">36 36 36 36 36 36 36 37 37 37 37 37 37 37 38 38 38 38 38 38 38 39 39 39 39 39 39 39 40</table>
<table name="#magicLevel">76 76 76 77 77 77 78 78 78 79 79 79 80 80 80 81 81 81 82 82 82 83 83 83 84 84 84 85 85 85</table>
</enchant2>
I tested it, and its enchantment increases the number of poison ticks.

Now, take a look at the skill’s parameter:
<enchant2 levels="30" name="Cost">
<table name="#count">11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40</table>
<table name="#activateRate">36 36 36 36 36 36 36 37 37 37 37 37 37 37 38 38 38 38 38 38 38 39 39 39 39 39 39 39 40</table>
<table name="#magicLevel">76 76 76 77 77 77 78 78 78 79 79 79 80 80 80 81 81 81 82 82 82 83 83 83 84 84 84 85 85 85</table>
</enchant2>
I tested it, and its enchantment increases the number of poison ticks.