Pachirisu Aggro Deck

If you go first: Attempt to get get a combo of Pachirisu Ex + Magneton + Dawn + Tool going. This will allow you to attack for 80 on your 2nd turn and likely KO any basic Pokemon the opponent put into play. If Magnemite is forced to come out but you are able to draw into the rest of the combo plus you have an X Speed on hand, use that X Speed before evolving into Magneton.

If you have a Rocky Helmet, put it on Pachirisu Ex immediately to deter attacks, but if you have the Giant Cape instead then put it on only the turn you can get enough energy to attack (unless you're in danger of losing Pachirisu Ex). Keep on building Magneton in the back to sweep with Magnezone later.

If you don't get the combo, consider sacking the active Pokemon, preferably with them wearing Rocky Helmet, and focus on building your backline. This may not be necessary to do though, so play it by ear.

If you go second: This is pretty standard play; put energy on either Magnemite or Pachirisu Ex if they are active, then if Magnemite is active and you have a Dawn + either X-Speed or Magneton, you can attack with Pachirisu Ex the following turn (hopefully with a Tool). Then you go back to the gameplan of attacking with Pachirisu Ex and building Magneton into Magnezone.

If you draw into a second Pachirisu Ex and have a spare Tool and Dawn in hand, then switch out the first Pachirisu Ex in the active slot when it's in danger of getting KO'd and use Dawn to get the second Pachirisu Ex immediately online. Otherwise just build it up normally alongside Magneton. This could bait out a Cyrus, which is good because your active Pachirisu Ex will remain healthy and there's one less Cyrus to worry about.

Dawn is very important to gaining tempo with this deck, so you definitely need 2 of her. Cyrus is replaceable with a 2nd Sabrina or even a Pokemon Communication (or vice versa: replacing Sabrina with a Cyrus or a Pokemon Communication).