I'm not sure what you mean by the "pulling in" but..:
Players
(Whatever)
Conditions
Always/(Depends)
Actions
Order [Unit] owned by [Player] At [Location] to [Move] to [Pull Location]
Perserve Trigger
This'll make the unit constantly move towards the "Pull Location"
For the explode one: add Perserve Trigger into the mix. There will be a 2 second delay beteen triggers so the sets of explosions will be 2 seconds apart. Allow for this in your maps. Repeat the explosion(s) several time in the same trigger if you have to.