Alternate powers seems to be an item of contention in all the campaigns I've been a part of, in part because some of the rules surrounding it are vague, and in part because of debate over what an "alternate" power is. Then there's the power-gamer point buy argument.
Power Gaming:
One might argue that a character with a freeze gun and a heat gun should have 2 separate powers: Blast (Heat) and Blast (Cold) with whatever side effects those blasts will have. Well Blast costs 2 points per power level, so both guns at PL 5 cost 20 power points. (Let's just use basic costs, never mind that they might be nested as devices).
Of course, a cheaper way is to have a gun that can blast heat OR cold, which is 11 power points, 10 for the blast, and 1 point for the alternate power.
This seems all well and good in this instance- you can't use both functions at once, if the gun is stolen you don't have the other gun as a backup, this is a fair use of alternate power.
The problem is that we run into some crazy edge cases- like using super movement: phasing as an alternate power of flight. Of course, you'd almost never need to use both at the same time- phasing involves going through solid matter, and flight involves going through the air- but how does this make sense flavor-wise? How do wings help you phase through matter, for example?
This seems to be a case of taking the powers in a way that's cheaper mechanically but doesn't make flavor sense. The justification for alternate power being cheaper is the ability to use only one at a time, and there may only be a few edge cases (phasing through the floor of an airplane) when you'd want flight and phasing active at the same time. To me, this is an abuse of point-buy.
An alternate power should legitimately stem from the base power. Using ice blast to create objects of ice is not too much of a stretch. Using ice powers to fly by blasting against the ground might be awkward, but understandable. Using ice powers to teleport is just silly.
Lasting Powers and Continuous Powers
There are some very vague sentences here in the handbook. A continuous power indicates that it remains on until turned off. A Lasting power states that it continues even if the user switches to an alternate power. So the question becomes: Does a continuous power turn off if you switch to an alternate power?
Let's say you're using Mind Control as your base power. You have the ability to mind control someone and it's continuous- it won't wear off on it's own- ever. However, you find yourself in need of switching to mind reading, to secretly read the mind of some other person- an alternate power.
Does the mind controlled person regain his senses at that time?
I am of the mind to say he does. While continuous powers do not require any active concentration on the part of the user, and he may be able to mind control a large group of people, I would contend that switching to an alternate power constitutes "Turning Off" the original power.
Now if this was a LASTING power this would be different. Using snare as an example, you could telekinetically snare a group of people, then switch to an alternate power to use TK to fly away without freeing those other people. But snare is LASTING, while Mind Control is not.
From a game balance perspective, you can have a character effectively using mind control and mind reading AT THE SAME TIME despite them being alternate powers- sure he can't gain control of a new person while he's actively reading a mind (he won't have enough actions to do so anyway), but he would not lose control, and could still issue verbal commands normally. Where is the mechanical balance to offset the fact that the second power costs only 1 power point?
Something to keep in mind with those alternate powers. Watch for LASTING power abuse, also. Be careful of people taking boost as an alternate power to ANYTHING. Boost is lasting, so they could boost up whatever they want for the duration of the boost, and it costs only 1 power point for the alternate power.
Extra Effort:
So this is another issue. Extra effort can allow you a temporary use of a power feat- such as alternate power. So with extra effort, you can gain an entirely different power (depending on how lenient you are with alternate powers being different from the base power).
Even without going crazy off theme (such as an Ice Queen using extra effort to turn her ice beam into a fire beam), you can add extras very easily. Maybe you want to add autofire to your power- normally that would mean cutting down the PL due to extra point cost- but not if you add extra flaws to offset- and since you know the situation, you can easily make flaws that "don't matter".
Let's say you have a heat blast, and you're fighting against a group of Slaver Runners from Iraq late in the night. You could add 3 points of autofire (+3 / level) and add in Limited: Only affects slave runners, Limited: only affects people from Iraq, and Limited: Only works during the night time. These limiteds do nothing to hinder your power, but give free points to gain extra with. Since the power feat only lasts for the encounter, you need not worry about ever having to use it in the day time or against a different kind of target. (This also holds true for uses of the inventor style feats).
I'm of a mind to either say extra effort cannot create alternate powers, or that it cannot give you the same power name (thus not allowing you to switch extras and flaws freely).
Alternate Flaws:
This is similar to the extra effort issue, but in advance. Blast is 2 points per rank, so rank 10 blast is 20 points. For 10 points you can take Rank 10 blast with (only works against women). Then take a 1 point alternate power to take a blast that only works on men instead. Sure, you can't use both at once, but unless you have an area of effect on it, you're only attacking 1 person per round anyway, and switching is a free action. You basically took a 20 point power and made it cost 11 points.
Result:
So this is why I've created my LAW of Alternate Powes:
1) Alternate Powers must thematically derive from the Base Power (GM Discretion). This prevents abuses like using teleport as an alternate of flight.
2) Alternate Powers must have the same FLAWS as the primary power. (So you can't use alternate flaws do double the value of your current powers).
3) Non-Lasting powers are considered to be "Turned Off" when you switch to an alternate power, even if they are continuous.
4) When using extra effort to create an alternate power, you may not add additional flaws to the new power. If you want to add extras, you will need to either lower the PL of the power, or remove existing extras from your power. (Mind- the lower PL could be offset with Boost).
Any other Alternate Power Laws I need? Let me know!