Instructions
Save the game before you enter Spear Pillar. This way, if you run out of Pokeballs or accidentally knock out Dialga, you can restart the Nintendo DS for another chance.
Bring the correct Pokeballs for capturing a Dialga. A Master Ball will instantly capture a Dialga, but there is only a single Master Ball per save file. Heavy Balls, Timer Balls and Ultra Balls are best-suited for taking Dialga. Heavy Balls are more effective when used on bulky Pokemon and Timer Balls should be used when the battle has dragged on for many turns.
Use Fighting- or Ground-type moves to deeply wound Dialga to bring down its health meter from green to red. Dialga is unaffected by Poison attacks and is resistant to Normal-, Rock-, Ghost-, Water-, Electric-, Dark-, Flying-, Bug-, Steel-, Grass- and Psychic-type techniques.
Inflict Dialga with a status-altering ailment to make it more susceptible to a Pokeball. The Freeze, Sleep and Paralysis effects limit Dialga's ability to fight back and increase the chances that a Pokeball will catch it. Do not attack it with moves that can cause Confusion and Burn, because they may make Dialga faint.