If you wanted to keep people from spamming a spell, you would not do it by increases the quests or grind required. The popular MMOs taught us how that goes. Time, ingredient, and mana limits are also only limits in numbers. The limits need to be an inherent part of the mechanic involved.
Polymorphing one's self should not be taken lightly because the user takes on all aspects of their new form; size, strength, limbs, senses, and in some cases the mind. A clacker player would not be able to wield weaponry or armour, speak to other players coherently, or even open doors. But that player would also be able to pass many monsters ignored, and enter tight spaces they would otherwise be unable. Or at least that's the ideal situation; most of this goes much farther than a graphic switch, as NPCs would have to treat the player differently based on current form and whether the NPC knew who the creature was. Same thing would apply to player perception, in that it shouldn't be obvious the polymorphed person is a player to other players.
The process can be explained two ways; an actual change in flesh, or a kind of planar swap. The flesh change follows conservation of mass, and would usually be applied to wearcreatures, the undead, and fantastical genetics. The second is the one seen more often, where the person's natural body is swapped out into a statis-inducing plane of reality, and replaced with another one (formed from raw chaos or prepared by the mage beforehand) where their "soul" stays. One could also describe it as the natural body being in semi-stasis and still capable of preforming thought functions for the new body.
In game, this would mean transformations are either slow and permanent, and instant and unstable. If the new body is indeed formed from a link to raw chaos, this would introduce all kinds of anomalies. Such as players finding it extremely hard to polymorph into anything resembling a living Yliakum creature, instead getting poor, chaos-corrupted imitations of what they were actually trying to achieve. If they are lucky or skilled at this point, they can use the body for a while, if a novice attempts it...
Heh, even without using amorphia as a fuel source, polymorphing is open to all kinds of
Fun.
