As an aeldari fanboy, I'm not sure whether I should be glad to see a reference to Isha or be filled with anti-Nurgle fervor. ;D
As JNA says, there's more bookkeeping complexity than needed, and some of these rules seem very annoying/punishing. Some thoughts:
PoorGravitasHandling wrote:
Till Death Do Us Part: At the beginning of your turn, if the Speaker of Ysha is not within 2" of your warlord, they lose one wound.
2" is pretty severe. That's one failed charge roll away from automatically damaging yourself. You could raise the range to 12" or 18" or what have you and retain the fluff effect I think you're going for (that Isha can't run away from Nurgle) while also making it much easier to use in practice.
The Cycle Empowered: The endless gladiatorial fight between invader and invaded strengthens both and benefits all. All enemy models gain a 6+ invuln against wounds dealt by plague weapons. Count each time an enemy model successfully makes this save and each time a plague weapon fails to wound a target of equal or lower toughness as compared to the strength of the attack.
Let Her Hone The Cycle: Every member of the Death Guard has a melange of diseases at their disposal. Sometimes their favorite just isn't the what it should be. Each time the count of The Cycle Empowered reaches 7 and after the currently active unit finishes it's attacks, reset the count to 0 and choose a Death Guard character you control from the HQ or Elites choices that is on the board. The chosen model gets +1 to wound with plague weapons the next time it attacks with a plague weapon this round. This ability may not be used on a model currently benefiting from any +1 to wound effect.
Waaaay too unwieldy. Your opponent will personally tear open a hole into the warp and go on an epic quest to rescue Isha just so they don't have to do all that bookkeeping. The idea here is that you want to reflect the push and pull of Isha coming up with a cure to Nurgle's contagions only for Nurgle to come back with something nastier the next time, right? How about something like:
"The Cycle Empowered: At the start of each battle round, you must declare that Ysha's power is waxing or waning. If waxing, friendly plague weapons suffer -1 to wound during the battle round. If waning, friendly plague weapons receive +1 to wound provided Ysha's power was waxing in the previous battle round."
So you can declare waning at any time if you just want your weapons to behave normally. You can declare waxing the turn before you need a power boost to gain a spike in damage on a critical turn. It does the whole, "My weapons are less effective some of the time but more effective the rest of the time," thing you seem to be going for but eliminates any extra dice rolling. The bookkeeping is just "is it waxing or waning right now?"