Pokémon Diamond and Pearl/Veilstone City

Veilstone City is the home to the fourth gym leader, Maylene.

Veilstone is home to the department store, so don't immediately worry about the oncoming Gym battle and lay back and go shopping.

Tasks

 * In a house towards the bottom of the city you will find a clown who will gladly hand you a Coin Case, you just have to select the correct hand that it's in.
 * Go to the Game Corner to get a total of 70 coins.
 * Speak with the man standing outside near the gym, and he will give you TM63 (Embargo).
 * Speak with the old woman on the first floor of the department store to obtain a mask of the starter chosen by Dawn/Lucas.
 * A clerk on the second floor will give you the Counter App for your Pokétch.
 * A man on the fifth floor will give you the Sticky Barb hold item.
 * HM02 fly, is in the Team Galactic warehouse.
 * A PP up beside the Galactic Veilstone Building.
 * On the house at the back of the Pokemon Center, talk to the man and he'll give you a Porygon.

Veilstone Department Store

 * 1F
 * Antidote
 * Awakening
 * Bubble Mail
 * Burn Heal
 * Escape Rope
 * Flame Mail
 * Full Heal
 * Grass Mail
 * Great Ball
 * Hyper Potion
 * Ice Heal
 * Max Potion
 * Max Repel
 * Paralyze Heal
 * Poké Ball
 * Poké Doll
 * Potion
 * Repel
 * Revive
 * Space Mail
 * Super Potion
 * Super Repel
 * Ultra Ball
 * 2F
 * Calcium
 * Carbos
 * Dire Hit
 * Guard Spec.
 * HP Up
 * Iron
 * Protein
 * X Accuracy
 * X Attack
 * X Defend
 * X Sp. Def
 * X Special
 * X Speed
 * Zinc
 * 3F
 * TM14
 * TM15
 * TM16
 * TM17
 * TM20
 * TM22
 * TM25
 * TM33
 * TM38
 * TM52
 * TM54
 * TM70
 * TM83
 * 4F
 * Bonsly Doll
 * Buizel Doll
 * Chatot Doll
 * Cupboard
 * Mantyke Doll
 * Mime Jr. Doll
 * Munchlax Doll
 * Pretty Sink
 * Refrigerator
 * TV
 * Yellow Cushion
 * 5F
 * Fresh Water
 * Lemonade
 * Soda Pop

Gym Badge #3

 * Black Belt Colby
 * (Lv. 23)
 * (Lv. 25)
 * (Lv. 27)


 * Black Belt Darren
 * (Lv. 25)
 * (Lv. 25)
 * (Lv. 25)


 * Black Belt Rafael
 * (Lv. 26)
 * (Lv. 26)


 * Black Belt Jeffery
 * (Lv. 28)


 * Gym Leader: Maylene
 * (Lv.28)
 * (Lv.29)
 * (Lv.32)
 * Reward: Cobble Badge, TM60 (Drain Punch)

Maylene is obviously a fighting trainer. Her gym is set up so you have to face most, if not all of the trainers here. Flying and Psychic are good against this gym, Flying the better since Meditite is also a Psychic. Also, using Fire attacks will work well on Lucario, since it is a Fighting/Steel.

Entering the warehouse
When you exit the gym after beating the gym leader, Dawn will appear again and say that Team Galactic has her pokedex and needs your help. Go to the Warehouse. After talking to Dawn, a 2-on-2 battle will be engaged.

Meteorites
Ever noticed the meteorites around Veilstone's western side of town? If you have in your party, touching one of the stones will change its form. The middle rock turns Deoxys into its Normal Form, the one above that into the Speed Form, and the two below that, from left to right, turn it into the Attack or Defense Form.