As a matter of fact, four characters have Final Smashes that are 100% identical to others:
Dr. Mario - Doctor Finale: Carbon copy of Mario's Mario Finale using giant Megavitamins instead of fireballs. The only differences are the fire visual and sound effects being replaced by normal ones. Hitbox, damage and knockback are identical.
Dark Pit - Dark Pit Staff: Copy of Zelda's Light Arrow. Aesthetically, it looks like a sort of laser beam rather than an arrow of light, but the hitbox, damage and launch attributes are identical. (Note that Sheik's Light Arrow is actually different in damage and knockback output, but still similar.)
Lucina - Critical Hit: 100% identical to Marth's Critical Hit in both aesthetics and mechanics.
Lucas - PK Starstorm: 100% identical to Ness's PK Starstorm in both aesthetics and mechanics.
Similar Final Smashes (they act similar, but have some slight differences and may have drastically different visuals):
- Shulk's Chain Attack and Duck Hunt's NES Zapper Posse are both very similar to Captain Falcon's Blue Falcon. Mega Man has basically a projectile version.
- Sheik's Light Arrow has more horizontal knockback and deals slightly more damage than Zelda's Light Arrow.
- Falco's Landmaster is less powerful but has more aerial mobility.
- Robin's Pair Up and Greninja's Secret Ninja Attack are very similar to Ike's Great Aether. The only big difference is Robin's start up part, having more range, but harder to hit.
- All Mii Fighters' Final Smashes are similar to others. Mii Gunner's Full Blast is nearly identical to Samus's Zero Laser, Mii Brawler's Omega Blitz is similar to Ike's Great Aether and Mii Sword Fighter's Final Edge is similar to Wii Fit Trainer's Wii Fit.
And I'm pretty sure I didn't cover everything.
