There are many Pokemon available throughout the game, here are some you may want to consider using:
- Gardevoir: Is a good replacement for Alakazam, as it knows some great moves (Psychic, Moonblast, Calm Mind, Wish, Hypnosis), and it should be useful as Dragon Types are gonna be more prevalent in the future.
- Galade is also great, learning great moves (Leaf Blade, Swords Dance, Close Combat, and Shadow Sneak through breeding with Duskull). It is a great set-up Pokemon with a fast speed and access to Swords Dance which is frankly speaking, amazing.
*Lucario fills more or less the same role, and just as well. Pawniard and Weavile is also good. In general all of these are better than Sceptile.
- Metagross: Again, a super defensive, but powerhouse Pokemon that can take and dish out damage easily, and has a great movepool (Meteor Mash, Hammer Arm, Bullet Punch, Zen Headbutt) and is a good addition to any team.
- The Eeveelutions are also great, though without TM's Glaceon and Espeon are probably the most useful.
You may want to consider replacing Sharpedo, possible replacements are Milotic, Feraligatr and Empoleon. There are a ton of great Pokemon out there