"POSSESSION: Give Deadman a power action and make a close combat or a ranged combat attack (as if he has a range value of 4) against an opposing target character as a free action. A successful attack deals no damage. Instead, remove Deadman from the battlefield and put him on his character card; the target is possessed, becomes friendly to your force and opposing to its owner's force, and any of the target's canceled powers return.
After the resolution of any action given to the target, you can release the target. Remove all actions tokens from the target and place Deadman in any unoccupied square within 4 squares to which the target has a clear line of fire. The target becomes friendly to its owner's force and opposing to your force.

If the target is possessed at the end of your turn, roll a d6 and add 1 to the result for each 100 points (or fraction thereof) of the target's point value. If the result is 6 or more, the target is released. If the result is 5 or less, deal Deadman 1 unavoidable damage.

Each time the possessed target takes damage, deal Deadman 1 unavoidable damage after the action is resolved. Any effect that can counter the target's powers can counter Deadman's Possession. If Deadman is eliminated or Possession is countered or canceled, the target is immediately released. Deadman and possessed characters can't be targeted by Mind Control or Possession.

This power cannot be cancelled."

Can he do this to anybody? like giants and colossals? and if so, If end up finishing the rest of my opposing characters force, using this power, does the game end?

Thank you in advance

Yes, he can do it to any character and yes, if you Possess your opponents last character, the game ends. So make sure if you do it, you have more points than they do.

Relevant entries on the subject from the Players's Guide:

Would be interesting to see him possess a vehicle, which becomes opposing to the vehicle's owner's force, then get's captured by an Arkham Asylum Guard which was originally a friendly character to the possessed vehicle...

uhmm what happens then? Does the original owner of the vehicle score points for capturing his own possessed vehicle? O_o what of Deadman then? or the pilot?