Shadow Toucannon

Look at that stare... never have I seen a bird with so much raw malice behind its stare before. What is it planning? What horrors does it intend to wreak out of sheer anger?

....not much. Shadow Toucannon has okay-ish damage output, but it's not setting any records. It's not the WORST investment early in the game, but it's not going to offer much raw utility.

Best PvE Offensive Moveset

• Peck is the only Fast Move recommended for offense, gets STAB, and suits a Flying-type role.
• Bullet Seed has no use.
• Rock Smash has no use.
• Drill Peck is the only meaningful Charge Move, with typing synergy and STAB.
• Consider Rock-type Pokemon instead of Rock Blast.
• Consider Meteor Mash Metagross instead of Flash Cannon. 

Best PvE Defensive Moveset

• Rock Smash is recommended on defense due to its coverage against Ice and Rock attackers.
• Peck gets STAB, making it best against neutral attackers and good against common Fighting-types. 
• Don't use Bullet Seed for defense. 
• Drill Peck is arguably the overall better Charge Move for defense due to how common Fighting-types are.
• Rock Blast can be used frequently to specifically hurt Ice-type attackers, but is also likely to be resisted by others.
• Toucannon isn't very tanky, and might faint before it can use Flash Cannon. 

None of Toucannon's Fast Moves are considered ideal, but Bullet Seed is generally recommended for its fast energy generation, letting Toucannon spam its Charge Moves sooner. Peck is a subpar move that offers below average gains, with STAB helping to bring up its damage output to average at best. 

Drill Peck is Toucannon's main Charge Move, with a low energy cost and respectable STAB damage. Rock Blast offers useful Rock-type coverage and can be used frequently, but its damage output is lackluster. Flash Cannon demands too much energy to be consistently useful, though its coverage against Toucannon's weakness to Rock and Ice Pokemon might catch unsuspecting opponents off guard.