Cacturne. Just look at that spooky scarecrow cactus! And it's dex entries:
X : "It becomes active at night, seeking prey that is exhausted from the day's desert heat."
Y : "Packs of them follow travellers through the desert until the travellers can no longer move."
Alpha Sapphire : "If a traveler is going through a desert in the thick of night, Cacturne will follow in a ragtag group. The Pokémon are biding their time, waiting for the traveler to tire and become incapable of moving."