You get the other two via dimensional rifts or in the post-game from Professor Laventon.
>Typlosion has the best Speed for more turns + Calm Mind (raises Atk, Sp. Atk, Def, Sp. Def) + Infernal Parade to inflict burn and deal double damage if enemy has a status ailment, redundant with Infernape, helps against Noble Lilligant, Electrode, and Giratina, can't get Quick Attack spammed
>Samurott has good Speed + only gets Swords Dance (Atk, Sp. Atk) + Ceaseless Edge is high crit damage and DoT, better than Empoleon, helps against Kleavor, Arcanine, Avalugg, and Giratina
>Decidueye's slow as shit + gets Bulk Up (same as Calm Mind) + Triple Arrows heightens critical rate for his next moves and is one of the only two guaranteed defense debuffs in the game (the other being Darkrai's Dark Void that also inflicts Drowsy), probably outclassed by Roserade/Lilligant (Victory Dance is the same as Calm Mind/Bulk Up but also gets +50% Damage)
Speed's pretty important in a Conditional Turn-Based combat system, especially if you can get 1v5'd, skipping Rowlet is probably fine.
