Clockwerk

Clockwerk is a long-range melee DPS commonly played as an initiator/ganker.

Gameplay
His first skill shoots out shrapnel fairly often over 10.5 seconds, dealing good damage and causing mini-stun. It is a very small aoe and not effective when multiple targets are near clockwerk, so it is beneficial to isolate heroes or hunt lone heroes down. If you can consistently hit one enemy hero over the 10.5 seconds, it deals an incredibly high amount of damage. His second skill is cogs, which basically sucks in units that are close to him and surrounds them with small structures. These structures don't allow anyone to escape and will push back heroes that try to get close them, which makes it very useful to combo with his first skill. Can also be used to run away or create an artificial wall, but this requires skill on the player's part. His third skill is a global rocket that has a decent aoe but slow travel time so it is difficult to hit from long range. It gives vision where it hits and deals some but not a lot of damage, making it effective to scout, harass, or kill a fleeing hero. His ultimate is a very long range hookshot which shoots out very fast from him to a target position. If the hook collides with an enemy hero or creep, he will be pulled to it and stun as well as damage nearby heroes. Very good for catching heroes that are running away or off guard, but takes positioning and skill to hit.

Source:

Tips

 * Scepter buff is actually extremely useful for him.
 * Rattletrap has 2 escape mechanisms, use them to enter fights, as well as getting away from them
 * Battery Assault works as a ministun so it's great for interrupting channeled spells or tps.
 * You get great map control with Rattletrap
 * You can also abuse the global cast range of Rocket Flare to kill fleeing opponents.
 * Rattletrap is a mortal threat to many heroes. But he gets weaker late game without items. So, farm.
 * You may spam Rocket Flare very early in the game from your fountain to scout for information on which hero is on which lane.
 * In the early game, a combo of Rocket Flare and Nature's Prophet's Teleportation can take out the opponent's courier if done properly.