One of the first things you should consider when building a Pokemon's moveset, especially for ingame, is to be careful not to overlap your Pokemon's attacks. Most Pokemon (with a few exceptions as I'll list below) do not need to have more than one kind of offensive move. For example, Serperior does not need three damaging Grass moves. When you use multiple attacks of the same type, you're limiting what your Pokemon can do to the opponent. Serperior cannot touch Pokemon resistant to Grass moves when it has so many Grass moves itself. It's better to have multiple kinds of offensive moves to get better coverage. That way, your Pokemon can take on many different opponents and you won't be forced to switch out and thus miss a turn.
Exceptions to this are numerous. For example, it is okay to use two attacks of the same type when one is a priority move. Priority moves like Quick Attack, Ice Shard, Aqua Jet, etc. are all great moves to pick off weakened opponents. It's great to use them on most movesets, especially ingame when you need to KO something that's been weakened by another teammate. Other exceptions are when a Pokemon needs an extra powerful move along with something that is reliable but does less damage. Sometimes you might be able to run something like Overheat and Flamethrower on the same Pokemon (Magmortar, for instance), with Overheat serving as a way to get a potential one hit KO when the weaker move, Flamethrower, will not OHKO.
It's also a good idea to look at your Pokemon's stats when making movesets for them. When you look at Serperior's stats, you'll notice that she's more of a Defensive Pokemon with great Speed. Her Attack and Sp.Attack are lower than effective sweepers. With that being said, Serperior is a great support Pokemon, but can also be a sweeper with the right moveset. Here are some examples.
if you want to run a Serperior set to support your team, you could consider using Reflect/Light Screen.
Serperior:
-Reflect
-Light Screen
-Giga Drain
-Glare/Leech Seed/Dragon Pulse
Reflect and Light Screen support your team by adding defenses to them for five turns. This adds to the longevity of your Pokemon.
If you wanted to run a sweeper Serperior, that's fine too, but you'll need the right moves to set up an effective offensive Serperior.
Serperior:
-Leaf Blade
-Coil/Swords Dance
-Aqua Tail
-Dragon Tail/Aerial Ace/Return/Leech Seed
A physical Serperior is outclassed by lots of other attacking Pokemon (Sawsbuck), but with a boosting move, it does fine. Here's another option for Sp.Attack:
Serperior:
-Giga Drain
-Dragon Pulse
-Calm Mind
-Leech Seed