Starting with D. Gren, his Prankster Ability allows you to set priority Spikes, Toxic, and Will-o-wisps, tho he is too frail for that. As an attacker, he greatly benefits from the sun, and can set priority Sunny Day. If you don’t already have a Sun setter, run Sunny Day, Solar Beam, Flamethrower and Switcheroo(If you run Focus Sash)/Synthesis/Taunt/Will-o-Wisp/Uturn. The item for this set should be Heat Rock, Leftovers, or Focus Sash. If you have a sun setter, swap Sunny Day for Dank Pulse or one the utility moves above. Outside of sun, replace Solar Beam with Giga Drain or Energy Ball and Sunny Day with U-turn running Choice Specs.
As a physical attacker, he has access to priority Swords Dance and can run Flame Charge, Sucker Punch/Uturn, SD, and Leaf Blade.
D. Lucario, I do not have much experience using, but for a special set, Extreme Speed/Vacuum Wave, Dark Pulse, Nasty Plot and Earth Power make for a nice set. Life Orb or Leftovers on this one.
For his physical set, you can run his Mega or run Band/Scarf/LO. Extreme Speed/Sucker Punch, EQ, Sucker Punch/Knock Off, Swords Dance(Don’t run if Choice Banded or Scarfed)/Drain Punch/Elemental Punches/Outrage/Zen Headbutt/Stealth Rock.
D. Snorlax is essentially Mega/Gigantamax Snorlax. It’s most powerful set is a counterpart to CurseLax, running Leftovers over Iapapa Berry and Belly Drum, EQ, Leaf Blade, and Drain Punch/Synthesis. Adaptability is viable n this set, tho many people choose Thicc Fat over Adaptability to negate it’s Fire and Ice weaknesses.
For a more stally set, you can run Leftovers Synthesis, Toxic, Bulk Up, Wood Hammer/other attacking move. 252 HP, 252 SpD, 4 in Atk or Def, your choice. The idea is to Toxic the opponent and Bulk Up till the physical side is unbreakable. It already is an amazing special wall, but you can drop something for Amnesia, tho is is almost never useful due to Lax’s tremendous Special bulk. Once this is set up, Wood Hammer crushes everything, and you can heal off recoil with Leftovers and Synthesis.
Note: these are all competitive movesets, and PP especially for Lax, may not last all the way thru E4. I had to use Ethers on Synthesis every 2-3 battles. That was in Hard Mode tho.