The meta: flyers and several maps that greatly benefit them. Tendrils of the Deep (TotD): Grounds flyers and is uncleansable for chasms. I don't think many people know how TotD actually works. Basically it is the inverse of Monsoon. It's key effect is that it will ground a unit as it leaves the AoE, so if you place it at the edge of a chasm tile any flyers moving out of the AoE will immediately cliff themselves. Damage: Monsoon is 8 in the AoE on cast, TotD is 8 on exit Grounding: Monsoon in the AoE on cast, TotD on exit Movement: Monsoon movement costs 2 in AoE, TotD costs 3 after exit The other thing to note is that TotD is an AoE spell that also happens to cause water. It is not a terrain effect and so is not removed by Naturalize etc.
The water is a terrain effect. The 8 damage, entangle and grounding is an AoE spell effect, like Cleansing Mist for example. So Naturalize will remove the water but not the rest.