My idea for a Maractus crest was to give it fairy stab/resistances as well as the pixilate ability effect. I like your idea of applying spikes on hit with certain moves though, I considered a layer of spikes on send out but with how that would ruin focus sash with no risk, your idea seems better. My main reason for fairy type was to have it be a kind of counterpart to the other cactus pokemon, Cacturn's dark type. Pixilate ability or something like it would be needed as Maractus learns no fairy type moves, but does get return and hyper voice, allowing for physical or special sets.