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, Lifting ST, Arm ST, 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 Move. 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.
For example, Groolor the space ameoba has spent no points on his point pool. Any Advantages granted to his template must be balanced by an equal value of Disadvantages. Groolor could have two legs and two short but extra flexible arms. If he wanted to have normal length arms (which must be extra flexible) he would need to free up 10 points by blob-shifting to -10 points of Disadvantages. In this case, Groolor takes one level of Ham Fisted (-5 points) and one level of Reduced Move (-5 points). If Groolor later spends 25 character points on his point pool he could take up to 25 points of blob-related Advantaged without corresponding disadvantage. He might take three normal length extra flexible arms, for instance.
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. Enhancements or Limitations which affect shapeshifting but not squishyness are at half value (since in effect they only apply to the 20 points above the cost of the Squishy advantage). Anything which suppresses the Squishy advantage prevents Blob shapeshifting. No Enhancements or Limitations at all can be applied to the point pool. For example, it takes 5 minutes for space amoebas to fully blob shapeshift. This is (approximately) five doublings of the normal 10 second time. This is represented by 5 levels of Takes Extra Time, but since it makes no sense for Squishy to take extra time the limitation is at half value or -5%/level (so -25% total, for a net cost of 30 points). A 25 point Blob Pool would still cost 25 character points.
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. Brachiator and Clinging are other examples of advantages that a blob shapeshifter could potentially learn. The ability to take a zero point feature or an additional disadvantage costs one point. No Legs (Semi-aquatic or Aquatic) are examples of potential additional Features or Disadvantages a blob shapeshifter could acquire.