Hold Item: Black Belt (boosts Fighting Type moves)
Weaknesses: Flying x4, Fire x2, Psychic x2
Strengths: Ground x0.5, Fighting x0.5, Grass x0.5, Dark x0.5, Bug x0.5
Heracross is an excellent Pokemon when it comes to strengths. Out or 17 total types, 5 of them only do 1/2 of their original damage. Although extremely weak against Flying types (they do 4 times the original damage), it can learn some Rock type moves such as Stone Edge and Rock Slide to compete against the pesky Flying types.
Being that Heracross is a Bug/Fighting type, its extremely weak against Flying types. So if it knows the attack Stone Edge it will be able to easily combat Flying type opponents. I believe Heracross is meant to be all out offensive. It has great Attack Power, great Speed, pretty good Defense and Sp. Defense, and a fairly decent Sp. Attack.
Because Heracross has great Attack Power, it should know Close Combat and Focus Blast. Two very powerful Fighting Type moves. And its Hold Item should be the Black Belt to make those two moves even more powerful. As previously stated, it should also know the move Stone Edge. Due to its strong weakness to Flying type opponents, it should be able to stand up to them pretty good as well. And as for the attack Megahorn. Heracross is also a Bug type and Megahorn is pretty strong Bug type.
Possible Double Battle Partners:
The partners for Heracross would mostly depend on your opponents team. Here are an example of what I am talking about.
Opponent Types: Psychic (Alakazam) and Fire (Typhlosion)
You: Heracross + a stong water type (Crawdaunt)
Since Heracross is part Bug type, if it used Megahorn against a Psychic type like Alakazam, it would do a great deal of damage due to the fact that Psychic types are weak against Bug types. And your teammate, Crawdaunt, it is a Water/Dark type. It would be a great match against the Fire type Typhlosion because it is weak against Water type moves. And Crawdaunt is a great Partner because it is also part Dark type. Meaning Alakazam's Psychic type moves would not effect it at all. Plus Psychic types are weak against Dark types as well.