The starting cost depends on what skills are on this screen.
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Its has place holders in Med, Necro, SS, and Focus. This pet will not have to pay for those skills.
To train this pet in Magery you would have to buy Magery and eval + 500 for the magic. 1501 points
To train this pet in Necromancy would only cost 500 points. It has Necro and SS.
To train this pet in myst, weaving, chivalry would cost 500 points. They have Focus or Med.
To train in necromage would cost 1501.
Some pets have a natural magic. Those only cost 1 point to activate the mastery. Use that one point if you want that magic. It will also use the magics masteries if you do.
My mystery pet is one that you should put Necro on. Its cheap and not many have it cheap.