Decklist from Negi, additional reading in the context of the 2005 format here.
This deck uses Delcatty as its main attacker, with Electrode ex to power it up. Delcatty's Max Energy Source does 10 damage for each Energy attached to it, much like Dark Tyranitar's Grind, minus 10 damage.
Supporting Delcatty is Magneton, combining to form a draw engine that was extremely popular in 2004. You use Magneton's Magnetic Field to get back a Lightning Energy from the discard, then discard that to Delcatty's Energy Draw.
Magneton and Electrode ex can also attack if the situation calls for it. Magneton's Magnetic Force does 10 damage for each Energy attached to ALL of your Pokémon, not just itself. Electrode ex's Crush and Burn lets you discard Energy cards for high burst damage. (Note that Electrode ex is misprinted, and should do 20 more for each Energy card discarded, not each Energy discarded, so Scramble and Double Rainbow only add 20 and not 60/40.)
Lead with Dunsparce (or Swoop into it) and use Strike and Run to put Jirachi and 2 other Basics on your Bench. Use the switch effect on Strike and Run to send out Jirachi, and continue setting up with Wishing Star.
Delcatty is usually the first Evolution you get, since it's the thickest line in the deck and you are most likely to draw it naturally. Once you get it out, you can start Energy Drawing to build up your hand. Don't worry about discarding Scrambles, as you'll be attaching them from the discard with Electrode ex anyway. Eventually you should draw into Magneton + Lightning Energy to complete the draw engine, and Electrode ex to put Energy on your attackers.
It's better to start the offense with Magneton, while powered-up Delcatty sit on the Bench. If you lose Magneton, you're only out 2 Energy, and Delcatty can jump in to revenge kill.
You should know how much HP your opponent's Pokémon have in order to plan how much Energy you need to commit to each of your Pokémon after Extra Energy Bomb. Try to set it up so that you can 1HKO or 2HKO. Don't forget to factor in damage-altering effects like Metal Energy and your own Double Rainbow Energy, and be aware that as you take more Prizes, Scramble Energy will go back to providing only one Energy.
Make good use of Swoop and Magneton to thin your deck of dead cards as a defense against Admin. Dead cards in the mid/lategame like Dunsparce and Jirachi make perfect fodder for Swoop or Magneton. Also, be sure to leave a Lightning Energy in your discard pile (instead of your hand/field) against Admin — if they Admin you, you can just discard whatever you drew for Magnetic Field into Energy Draw. In contrast, if you don't have Lightning Energy in your discard, you have to topdeck an Energy card in order to Energy Draw.
This deck runs a very low Supporter count, relying on Dunsparce for early-game setup and Delcatty for card draw in the mid-/lategame.
Since this deck plays Heal Energy, remember you can use Jirachi's Wishing Star, attach Heal Energy to wake it up, then retreat. The Heal Energy can be gotten back later with Electrode ex's Extra Energy Bomb, but note that the healing effect will not occur, since it was attached from the discard pile instead of the hand.
This deck plays 4 Swoop! Teleporter. Its uses are detailed on my other site.
This deck also plays 4 Surprise! Time Machine. Its uses are:
Resetting Delcatty/Magneton's Poké-Power. This is by far the most common use, and the reason the deck can get away with a low Supporter count: each Time Machine basically reads "discard an Energy card to draw 3 cards".
Removing Special Conditions and other effects of attacks.
Suiciding a Pokémon (for Pow/Scramble) if there's enough damage on it to KO the Basic.
Note that if you Surprise something and it has Double Rainbow or Scramble Energy attached, those will fall off, so avoid doing that.
(This deck plays 4 out of the 5 Rocket's Secret Machines, all except Venture Bomb. This is just interesting trivia, and has no effect on gameplay.)
TV Reporter: Discard outlet for Energy or dead cards in the lategame. Functions like (and would replace) Surprise! Time Machine, giving you one more draw 3 + discard 1 effect for the turn.
Delcatty ex: Lategame attacker. Upstream can do a lot of damage if you've lost a lot of Pokémon (and their attached Energy).
Holon Energy GL: Damage reduction against ex's. You could also add Grass Energy for immunity from Special Conditions. Putting Grass Energy + Holon Energy GL on Jirachi means you can use Wishing Star without falling asleep.
Poké Ball, Master Ball: Alternative Evolution searchers.
Holon Energy FF + Fire Energy, Ancient Tomb: Negates Weakness.
This deck has a lot of answers to Cessation Crystal: 4 Windstorm to get rid of it directly, and 4 Cyclone Energy and 3 Pow to turn it off by sending the opponent's Active Pokémon to the Bench.
This deck has a surprisingly high number of Basics that can paralyze or prevent attacks. This is your main defense against opponents with attacks that prevent you from using Powers (Jirachi ex) or Trainer cards (Manectric ex, Dragonite ex δ). If you brick in the early-game, you can buy turns to get back in the game by flipping heads on your Basics' attacks.
This deck is soft to Cursed Stone, as both Delcatty and Magneton have Powers and an unimpressive 70 HP. This deck also runs no Stadiums of its own, making Windstorm the only counter to Cursed Stone. Decks with both Cessation Crystal and Cursed Stone (e.g. Rai-Eggs) can really strain your answers.
It is very easy to run out of time on TCG ONE with this deck. You'll be using many Powers as you have multiple Delcatty/Magneton/Surprises, and you also need to do mental math to decide how to distribute the Energy from Extra Energy Bomb. On the other hand, if you are a combo player who enjoys taking long turns and sequencing optimally, this deck would be suitable for you.
Every Pokémon in this deck other than Jirachi is weak to Fighting.