Spawning particles at an entity or player no longer works.

/particle lava ~ ~1 ~ 1 1 1 0.5 2 entity @e[type=Chicken]

This only spawns particles at the command block or player that ran the command. The particle command syntax now shows [mode] as the last input. I'm not sure if players are now intended to run an /execute command to spawn particles at an entity or if this is a bug.