Multiple weapons: on the character sprite, make another animation and call it as the new weapon. copy all of the frames from the default animation and paste them in the new weapon animation. then edit them in the picture editor so the character is holding the new weapon. go to event sheet editor and make a new event:
On (character sprite) collision with (new weapon sprite)
Then add an action to it:
(character sprite) Change animation to (new weapon animation)
And another action to it:
(new weapon sprite) Destroy
Thats how to change the look of the character. Make sure you make the same event, but with the original weapon and with the default animation, so you can change back to the original weapon as you walk over it.