If you are looking for neutral coverage (which should probably be specified separately than just "coverage") Poison Jab isn't nearly as good as Return, which is available to everything. There simply aren't enough Grass Types in-game to justify losing the extra power.
Frankly, if you are talking about "coverage" moves for Maractus, listing Aerial Ace makes more sense than listing Poison Jab.
Not to mention immunity isn't that big a deal when all in-game Grass-types resist it anyways.
Frankly, if you are talking about "coverage" moves for Maractus, listing Aerial Ace makes more sense than listing Poison Jab.
But honestly, how many Water attacks are you going to see in-game? There's no real Water gym this time around, and the only surfing areas are completely optional. The only particularly relevant Water types are some Duckletts and Swanna in the Flying Gym, Shauntal's Jellicent, N's Carracosta, and Ghetsis' Seismitoad.Maractus also gets the very nice Water immunity, for what it's worth.
Not to mention immunity isn't that big a deal when all in-game Grass-types resist it anyways.