Jirachi, the Wishing Pokémon has enjoyed a healthy degree of popularity throughout the generations. Psychic-Steel is a very good typing, and Serene Grace is heavily abuseable with the right moveset, which Jirachi most certainly has. Base 100 stats across the board is still a decent stat line, allowing Jirachi to perform decently at a multitude of roles. However, that stat line remains decent. Jirachi's fast, but there are plenty of faster threats. Base 100 offenses are useable, but without any powerful setup moves, Jirachi is lacking in power to be a sweeper. 100 HP is... actually pretty good especially in conjunction with 100 defenses, but is not excessively so and Jirachi can be broken through by more powerful threats with ease.
A Supporting Wish
Jirachi
Item: Leftovers
-Iron Head/Body Slam/Thunder
-Wish
-Stealth Rock/Protect
-Encore/Toxic/Thunder Wave
Nature: Impish (+DEF, -SATK) or Bold (+DEF, -ATK) or Jolly (+SPE, -SATK) or Timid (+SPE, -ATK)
EVs: 252 HP/4 DEF/252 SPE
Jirachi has a multitude of moves to harass and disrupt your opponent while acting as a cleric for your team. Base 100 HP Wishes with max health investment are the 2nd most potent wishes in the tier (after Blissey's monstrous Wishes), capable of healing Toxapex and Rotom 2/3 the way up, Ferrothorn and Kommo-o 57%, Tyranitar 59%, (assuming Max HP investment on everything except Tyranitar) which is pretty nice considering most of these don't have any natural recovery outside of Leftovers and Rest. Stealth Rock is a great support option, but if you already have a dedicated Rock setter on your team, Protect to give Jirachi longevity and scout for moves and combos well with Toxic. Encore locks your opponent into a move turning it into setup fodder for Jirachi's teammates, Toxic sabotages bulky threats while Thunder Wave makes speedy threats more manageable. Offensive move is mainly to prevent Jirachi from becoming Taunt bait. Iron Head is great for flinch hax, though is weak without investment (still can 3-4HKO anything that doesn't resist/excessively bulky). Body Slam and Thunder have a respectable 60% chance to paralyze and can be chosen in lieu of Thunder Wave.
Other Options
Healing Wish -sacking Jirachi hurts, but curing Urshifu's Burn or Dragapult's Paralysis can win you the battle on top of the full heal.
Reflect/Light Screen -Dual Screens are always an option, but better in doubles
Substitute -good move and Jirachi has bulky 101 Subs, but Infiltrator Dragapult is definitely a possibility and will wreck Jirachi easily behind a Sub
Calm Mind -Jirachi's best offensive setup move and it has the movepool to abuse it, but runs hard into 4 moveslot syndrome when trying to setup