I'm going to try something new here. I'm looking at running an M&M game in the near future that will make extensive use of Alternate Form, Summon, and Sidekick. Rather than have the Weavers give me a laundry-list of how these things can be exploited, I want you to show me. Give me a character built around one of those three options -- Alternate Form, Summon, or Sidekick -- designed to make a GM pull his hair out.

The characters are PL 6 w/ 90 CP. You can trade-off up to half again campaign maximum, so Toughness of +9 and Defense of +3 (or the other way around, naturally).

Well, the classic break for Summon looks something like this:

Summon (Minion) 1 (Extra: Horde)(Power Feat: Progression x9 (1,000 minions) (12 Points)
Minions:
Attack Focus (Ranged) 7
Dodge Focus 4
Equipment 4
-Assault Rifle (+5 Autofire, 50', 16 EP)
-Tactical Vest (+4 Toughness)

Attack: 0 (+7 Ranged)
Defense: 14 (10 Flat-footed)
Damage: +0 Unarmed, +5 Autofire Assault Rifle
Toughness: +4
Fort: +0
Reflex: +0
Will: +0

So you summon all your minions with a standard action, then order them to make a Combined Attack on somebody you realllly hate with your move action. So they make a combined attack for +1003 damage. Plus autofire.

All yours for the bargain cost of 12 points!

Minions is a good example, sidekick is harder to abuse but TV gives us the UR-Example: Doctor Draken from Kim possible and his sidekick Shego!!!

Sidekick gives you a single minion with CP equal to 5 times your rank.

Theorethically, that means that if you're at power level 6 you can buy up to 6+5 ranks (11 ranks max) in sidekick (so in this case 55 point minion+drawbacks for more points)

In other words, for a measly 28 points making stats for Shego. She has 16's in all physical stats, 14 int, 14 will and 14 cha and you still have plenty left over to give her blast, invulnerability and more with maxed out combat statistics and all the skills she needs.

Seriously sidekick allows you to make a character more powerful then your PC. Your Pc will be a raving bumbling egomaniac failure at being a gadgeteer mad scientist and you'll have a kung fu fighting, energy blast throwing, super-thief, unkillable (seriously Shego is unrealistically tough when you look at what she survives), deadpan snarker dark action girl!

Duckman and Decoy the boy wonder?

Well, Shego was the only constantly competent antagonist in all the show. Though Draken had his moment in the sun in the movie when he built an army of mecha and came within an inch of conquering the world. That said there was a three parter where Shego became supreme overlord and made Draken her dragon just for giggles.

Never understood why she didn't just go solo. She never seemed to actually have any use for Draken except to pay for her trips to various luxury spas...

Well I was making reference to the batman spoof on tiny toons, plucky played batman and hampton pig was robin, who was in the classic duck dodgers sense was competent and skilled, so plucky has him in a suit bedecked in targets and he without fail got tossed at the bad guys.

don't remember that cartoon. But Kim Possible was always fun for chuckles on a lazy saturday morning

Isn't that assuming they are actually capable of FITTING in the space you are trying to summon them in, as well as actually being able to simultaneously fire upon the same target (if said target is not airborne and pretty much overhead)? Mechanically that break is sound, but the only player trying to pull this trick off in actuality is the one who rolled a natural 1 on his Knowledge (Common Sense) check. Even in the comics that give M&M so many of the excuses to ignore physical laws, that sort of thing has so many limitations it isn't even attempted except by D-list villains who get curbstomped as the prologue to the main story!

Alternate form is easily breakable simply because you can apply flaws directly to the alternate form power, thus offsetting the number of pp you need to spend to get 5pp in powers for the form.

For example, the default action is Free. That means you can easily apply the Action flaw 3 times (Free --> Move --> Standard --> Full) and reduce the cost to 2pp per rank. Since Alternate form is not capped by PL (unless the GM rules it so) you can go ahead an buy 20 ranks in it. Thus, you can get an additional 100pp to spend on powers for only 20pp.

Other likely candidates for abuse include Unreliable, Side Effect 2, Check Required*... I have seen players submit characters that have alternate forms that cost 1pp per *3* ranks. That mean 20 ranks, giving 100pp, only costs 7pp...

It is really easy to get an Alternate Form that nets you far more pp than you spend on it.

*yeah, I know, Check Required is the cheesiest flaw ever and no sane GM allows it, just including it because I have seen it used for just this sort of optimization.

Hah! Become Freeza! Hide a transformation power inside the transformation power that's inside your OTHER transformation power.

Hilarity ensues.