I mostly play Cinderace, Greninja and Zeraora, not only for ranked, for fun too, all physicals, so special glasses are still lvl 1 LOL.
I never liked Gengar before, I disliked SludgeHex combo cause is easy to avoid and i dont like a strightfoward pattern of gameplay when you do the exact same mashing buttons with no other interaction at all.
Shadow Ball Dream Eater has a fun interactive gameplay with little trick here and there, i will explain for you why im so glad with this new discover (for me):

·Shadow Ball is a low cooldown move that reduces sp def and slows for a little time, but is a really high slow. SB needs to be aimed, and the low cd makes it more fun to play to poke/engage with it.
·Dream Eater puts the enemy to sleep and you can recast to teleport to the sleeping target, dealing damage and healing yourself. If you succesfully land the move, you can decide what to do next (fast), so its really fexible. If its too risky, you hold back, if the target can die, you go in, you need healing? you need to move away to dodge something? DE got you homie.

The second cast of Dream Eater reduces the cd of your Shadow Ball, so if you combo correctly, you can do SB>DE>DE2>SB for a fast combo.
You also can time it to do a 3 SB combo, SB>AA>DE>AA>SB>DE2>SB, and I promise, its not difficult.
Gengar SludgeHex build is really glass cannon, but SB DE has sustain and DPS, Flexibility and CC, its really really fun to play also !