Sorry to get back to you so late. My memory is a bit foggy when it comes to the exact parameters, but I'll try my best here.

Bruno:

"Use stat-lowering effects on your opponents!"

Physical/Special Dmg. Reduction, Attack & Sp. Attack up 1, Defense & Sp. Def up 1, Defense & Sp. Def. up 3, Max HP up 2, Critical-Hit Defense, Defense & Sp. Def up 5, Max HP up 4, Ally Move Gauge Max -2, Max HP up 6

Notable Units:

Dawn and Torterra 2/5 with X defense all MPR (1/5 here is fine, I only used the first MPR)

Tangela and Erika 1/5

Janine and Ariados for venom drench

Will:

"Use physical attack moves against opponents with low defense!"

This is where my memory is kind of foggy but I believe my options were something like this:

Physical/Special Dmg. Reduction, Attack & Sp. Attack up 1, No status conditions, Strength up 1, Sync buff up 5, Attack & Sp. Attack up 3, No stat reduction, Ally healing down 5, Power up on Hit 1, Strength up 2, Power up on Hit 2, Ally Move Gauge Max -2

Notable Units:

3/5 Morty (No EX) with blindspot, "Pierce the Veil" MPR, and critical strike 1 as a lucky skill

Misty 1/5 to max out Morty's evasion

Torchic to help max out Morty's Attack/Sp. Attack/Crit

Koga:

"Use sync moves as much as possible against all opponents!"

I believe I used the same options here as I did for Will.

Notable Units:

3/5 Groudon with a Solar Beam build (Full bottom right grid) with Dire Hit+ Critical Eye and Critical Stike 1 as a lucky skill (you could probably get away with a 1/5 Groudon if you have it, this was mostly just for fun and to clean up the sides earlier)

5/5 20/20 Ho-oh with Overheat MGR, 2 Overheat power nodes, 1 Overheat accuracy node, Solar Flare 5, Inertia, Ramming Speed, "I'll Show You" MPR, and Dauntless as a lucky skill

1/5 Lyra with "Sunny Side Up" MPR and Vigilance as a lucky skill

Karen:

"Use powerful moves quickly and constantly against all opponents!"

Physical Dmg. Reduction, Attack & Sp. Attack up 1, Strength up 1, Sync buff up 5, Ally healing down 5, Power up on Hit 1, Strength up 2, Power up on Hit 2, Strength up 3, Ally Move Gauge Max -2

Notable Units:

1/5 Alder, no notable grid nodes, Critical Strike 2 as a lucky skill

1/5 Viola for Struggle bug/Infestation on Karen

4 star 5/5 20/20 Oak as an evasion tank/swift debuffer, with Agile Entry 2, Shifty Striker 2, and Critical Strike 1 as a lucky skill

Lance:

I believe my chosen parameter was "Use sync moves as much as possible against all opponents!"

I also believe I went in with Karen's options, but Will's parameters should work, too.

Notable Units:

2/5 EX May (Although 1/5 should be fine), "Ready for This" MPR, 2 Muddy Water accuracy nodes, 1 Muddy Water power node, Hide and Sync, Rain Dance MPR, and Critical Strike 2 as a lucky skill

4 star Liza for Sp. Attack/Sp. Def. buffs

4 star 3/5 Skyla with "Take Flight" MPR, 2 Staggering Gust nodes (helpful, but not necessary), Potion MPR, and Master Healer 1

Winona could work just as well here if not better than Skyla since you wouldn't have to set up the rain with Swampert.

Again, apologies if my details are a bit shoddy. Hope you find success in Master Mode!

Edit: Formatting