(target yourself so you can release an attack through power move)
Under the current rules, in order for an arcane magic user to cast a Power Move he must first cast that Power Move on someone, granting that person the ability to use the Power Move when they are next able to (as limited by the spell's duration. You may also maintain the effect to allow the character granted the Power Move the ability to use it over consecutive turns). For example, a mage that wishes to cast a fireball would have to cast Power Move on himself and
then release the fireball from the Power Move (which I believe he is allowed to do as part of the same action). If he tried to cast Power Move on an enemy he would be granting that enemy the ability to use the Power Move instead (see the note box below Magic, Arcane on pg. 50). This is how I understand the rules anyway. Magic attack allows you to make
direct spell attacks against foes, but cannot grant allies the ability to use Power Moves like the casting of Power Move can.
TheGreyReversed wrote: Also I am a huge fan of FMA and so I was reffering to there method of alchemy.
If I remember correctly, Fullmetal Alchemist uses transmutation circles (I've only seen two episodes as I don't have cable, so if I'm incorrect in any of my assumptions or approaches I apologize). There are a number of potential ways to simulate alchemy from FMA, however, as it seems you're interested in using the Invention ability I'll use that as a starting point.
Alchemy through Invention
While Invention is best suited for representing more 'realistic' alchemy, it can still be adapted to simulate more dynamic forms of alchemy such as those shown in Fullmetal Alchemist. The first, and most dramatic, change needed will be adding a special defect that causes the Invention ability to cost endurance. A weakness such as the following would likely suffice...
Extra Endurance Cost
One or more of your abilities costs additional endurance to use. At level -1 the ability costs 5 more endurance, at level -2 it costs 10 more endurance instead, and at level -3 it costs 20 more endurance instead. You need only pay this extra cost when the ability is activated, and need not pay it to maintain the ability. If the ability has no endurance cost to activate, this weakness causes it to have the listed endurance cost to activate at all times. If this weakness is tied to a Barrier ability it affects only the barrier's activation cost, not its cost to "buy off" damage.
With this special weakness you can allow your players to determine how good they are at alchemy by choosing 1, 2, or 3 levels in it (hint: most alchemist characters should have 2 levels). The lower the level in Extra Endurance Cost, the more times they can transmute during any given encounter.
The next step I would suggest is simply reinterpreting the way Invention is used. You have the right idea with counting environmental objects as the components, however, I would also double the DN of the invent attempt when attempting to use components that do not quite fit what they are meant to be transmuted into, but are still reasonable (such as creating a steel shield out of metal filings in the sand). I would also suggest tying the Invention ability to 1 level of Trigger: Draw Transmutation Circle, or some other such catalyst, and causing any alchemy transmutation attempts to be delayed until the end of the round, (this delays alchemical transmutations as though they had the Slow flaw, and represents the fact that, for the greater part, transmutation circles and other such catalysts cannot be created instantly).
As far as determining damage and creating transmuted objects that simulate abilities, it's fairly easy and already included in the Invention rules. If you look closely at the Invention DN chart you'll notice listed numbers preceded by a '+' (+1 for DN 6, +2 for DN 8, +3 for DN 10, etc.). When creating an invention you may attempt to make it with a total number of simulated abilities up to the listed bonus number. For example: you could make a strong DN 6 weapon by giving it the Weapon ability at +1 (which would have it deal 2 damage, 1 for Weapon +1, and 1 default damage), or you could make a powerful DN 10 flame-thrower by giving it the Power Move ability at +3 (remember, though, that you still must pay the separate endurance cost for the Power Move). You can even combine different abilities and weaknesses so long as the total value does not exceed that allowed for the DN (presumably you could give DN 2 and 4 inventions simulated abilities and weaknesses so long as the point total is not greater than 0). To determine how well the attack of such a creation hits use the character's normal attack roll (usually based on the Combat Skill ability).
While this method does stretch the Invention ability a little, as some transmutations may not actually be physical objects, it still works well enough.
Alchemy through Magic
As an alternative that is more in keeping with OVA's magic system you can just use the Magic, Arcane ability as is, and create a transmutation ability such as the following...
Transmutation
You possess the ability to alter the shape and properties of an object, changing it into something new. For a cost of 10 endurance you may change one or more non-living objects, or a part of a non-living object, into a new object of a roughly similar size, mass, or substance (as the GM deems appropriate). You may use the collective properties of components used for the transmutation and may even transmute multiple objects out of larger components. You cannot create living creatures through this ability. You may give objects made using transmutation simulated abilities and weaknesses, though the total collective value, for all objects created with one use of transmutation, cannot exceed your level in Transmutation. When you use this ability roll your Transmutation dice, plus any dice from appropriate abilities such as Smart, against a DN equal to 2+ double the value of simulated abilities and weaknesses granted to the creation (the DN cannot be reduced below 2 as a result of granted weaknesses). If the created object does not fit the size, mass, or substance requirements provided by any of its components, but the GM decides that the creation is still reasonable, the DN to create the object is doubled. If this check to create a Transmutation fails, endurance is still spent and the created object is only partially transmuted, causing the components to be ruined, and creating an object that is either completely useless or that falls apart. If this ability is used through the Magic, Arcane ability you need not roll to determine if the object is created, instead the Transmutation automatically succeeds if the casting succeeds.
Misc. abilities in alchemy
While either of the two methods above will adequately portray the majority of Fullmetal Alchemist's powers, some powers can, and should, be represented using the normal OVA abilities. For Example: Roy Mustang (if I remember the character correctly) can have his fire powers represented primarily through a Power Move. Though he technically uses transmutation, you do not need to use transmutation abilities to properly portray his powers. You could simply construct Roy's powers as follows...
Power Move +3
Fire Attack (don't know the proper name)
Area Effect, Continued Damage, Ranged, No Knockback, Requirement (oxygen environment), Slow, Affinity: Fire; 20 Endurance.
Special Ability: Fire Control +1 (May create fire and control it to an extent)
Endurance Reserve +3 (Permanent Transmutation Circle)
Focus: Permanent Transmutation Circle -2 (Power Move, Fire Control, and Endurance Reserve dependant on Permanent Transmutation Circle).
I hope that helps (and I hope I didn't get anything too terribly wrong). These suggestions are not play-tested, so if they feel unbalanced adjust them to taste.