Spear Pillar is based appears in Diamond and Pearl and is where you battle Palkia and Dialga. In Brawl, either Dialga, Palkia or Cresselia appear in the middle ground of the stage and each uses their own attacks which can get in the way and damage players.
Palkia uses Spacial Rind causing a beam of energy to hit the stage, makes the stage turn upside down, makes the stage break away in certain areas, reverses the controls or slows time. Dialga uses Roar of Time causing a beam to appear from random locations which attacks players or turns the stage on it's side and Cresselia uses Psycho Cut causing a crescent boomerang to either fly around hitting people to shoot waves of energy.
Azelf, Mespirit and Uxie also appear in the background flying around.