You are an amorphous blob, like an amoeba, and can create new pseudopod limbs at will and absorb old ones. You cannot make cosmetic changes and are subject to mass conservation. You can freely modify your template with the following advantages and disadvantages, up to the limit of your point total plus the point pool you have for shape shifting: Extra Arms (must be extra flexible), Extra Legs, Payload (up to level 20), Striker (crushing, weak), Terrain Adaptation, Amphibious, Aquatic, No Legs (Bounces, Rolls, or Slithers), Missing Digit, One Arm, No Fine Manipulators, Bad Grip, Ham Fisted, One Hand, reduced Basic Speed. You cannot otherwise change your template. All your arms must be extra flexible, including the two you get for free (this uses up 10 points of the available pool when you have two arms, 5 points when one armed). Arms cannot be long. In addition, you can change your general shape, forming a pillar, slumping into a patty, flattening out into a pancake, or squeezing through openings only a few centimeters across, but this is not morphing - you still look like a blob. You can morph away crippled limbs, and can morph new limbs into existance to replace severed/crippled limbs. The total bonus to ST from lifting or arm ST cannot exceed 30% of the your natural ST.
It takes ten seconds to alter your template. Relatively minor changes may be accomplished in less time, at the GM's option - turning a striker into an arm, or a leg into an extra arm with the foot manipulator disadvantage, would only take three seconds, for example. If asleep, knocked unconscious, or killed, you revert to a "natural" form which has No Fine Manipulators, No Legs (Rolls or Slithers), and Basic Move 1.
Blob characters are unusually squishy and flexible. The Blob trait includes all the benifits of the Squishy advantage. You cannot take both.
You can freely spend character points to increase the extra character point pool available for your blob shape changes. Characters with Shapeshifting (Blob) commonly also have Stretching, Soft, and Invertebrate, but this is not required (a hydrostatic skeleton and muscular hydrostats, for example, could explain why you do not have the trait Invertebrate; hard nodules on your skin could be the reason you are not soft).
With the GM's permission, you can train yourself to shape your body in such a way as to gain selected other exotic physical advantages. You must pay 1/5 of the point cost of that advantage to have access to it, once you have access to the advantage you can shapeshift into a form with that advantage by using the points in your blob pool. This advantage must be able to be explained by gross changes in physical shape. For example Groolor, the space ameoba, wants to learn how to shape his body into an airfoil. He takes Flight (gliding -50%). This would normally cost 20 points. For 4 points, he can gain access to gliding flight. By spending 20 points from his blob pool, he can form a gliding airfoil and glide gently to the ground. Lifting ST, Arm ST, Brachiator and Clinging are other examples of advantages that a blob shapeshifter could potentially learn.