Spelven's low 50 Speed in combination with her Psychic/Ghost typing makes her 4x weak against Ghost and Dark types. (This is especially troublesome, given that Gengar, Houndoom, and Necrosia all frequently appear in higher level battles in the main storyline and a lot of other Pokémon carry either a Dark or Ghost move like Rampage, Dark Resolve, Shadow Clamp, or Dark Pulse.). Regardless, Spelven is still a solid Pokémon to use, thanks to her expansive array of coverage moves, such as Heat Wave, Hydro Pump, and most notably "Focus Miss"/Focus Blast for Dark types, all alongside an excellent base 115 Special Attack. In addition, Recover and Calm Mind are also nice moves to have for setting up.
Overall, while she does have two very glaring weaknesses compared to Hantama's Intimidate, Spelven makes up by having a very good movepool and relatively better bulk than Hantama.