Total registration numbers:

Melee Singles: 1,692 entrants (decreased by 136 entrants from G3)
Melee Doubles: Approx. 115 teams (decreased by 282 teams from G3)
Wii U Singles: 1,007 entrants (decreased by 89 entrants from G3)
Wii U Doubles: 90 teams (decreased by 182 teams from G3)
64 Singles: 176 entrants (decreased by 62 entrants from G3)
64 Doubles: 9 teams (decreased by 38 entrants from G3)
Rivals of Aether: 96 entrants
Street Fighter V: 82 entrants
Towerfall: 35 entrants
Catherine: 25 entrants

Total: 3,108 entrants (attendance decrease of 484 total)

Notably not registered (going off their respective rankings):

Melee - PPMD, Hax, aMSa, Wobbles, Kage, Zanguzen, Redd, lloD, Sung666, Darrell, $mike, Swift, Porkchops, I.B, OkamiBW, Smuckers

Smash 4 - Trela, iStudying, Megafox, Ryo, Seagull Joe, and more (please inform me, I don't know much about Smash 4 top players lol)

64 - Stranded, Star King, and more (once again, I don't know much about 64 top players lol)

Notable international/rare attendees:

Melee - Armada, Leffen, Lovage, Rudolph, Android, pheX, watch, Professor Pro, and more

Smash 4 - Ranai, Abadango, FOW, Kameme, and more

64 - wario, Alvin, Isai, SuPeRbOoMfAn, and more

Notably not registered Melee - PPMD, Hax, aMSa