I don't think you can but on s/g/c you could put a male alakazam and a female Meganium into the daycare and the egg would be a celebi, would you be able to that on this?
that was just a stupid rumour thats been going about since the days of g/s/c, just like the "0mgzzz LyK TotALly UuZe SweEt ScEnT At dA ShRiNE n U'lL gET a CeLeBii LOLZZZ." celebii is/was only available through a nintendo event and by no other means. and why would breeding two completely different pokemon together breed a third completely different pokemon ? just cos one's psychic and one's grass doesnt mean you'll get a psychic grass type as an egg. think it through.