Petrifying Prison should be an important spell in Wands (given how easy it is for players to teleport out of the way of projectiles), however, It has a few issues which make it difficult to balance:
1) If your opponent has Leap then Petrifying Prison is almost useless and wasting a spell slot.
2) If your opponent doesn't have Leap then Prison becomes very powerful, which is what led to its recent cost increase. Now it is barely used or mentioned.
The fundamental problem is that its utility is binary. It either turns Teleporting ON or OFF. It is pure rock paper scissors, with little room for skill to compensate.
How can we fix this?
I propose a slight modification to how Prison works...
...namely, anyone can Teleport away from inside Prison at any time, but doing so does damage (and destroys the Prison). NOTE: this damage must be less mana efficient than other spells whose primary purpose is to do damage. Also, Leaping would no longer be a hard counter to Prison and should incur the same damage penalty when used. To feed back this concept visually, I suggest adding inward pointing spikes to the existing Prison mesh.
How would this change how players use Prison?
Instead of being prevented from teleporting, trapped players would have an interesting cost/benefit analysis to make...is it better to stay put, gain a mana advantage and try to deal with incoming attacks, or take the damage and escape, thereby granting the Prison caster a minor victory? This decision making process remains active for the duration of the spell...at any point the imprisoned wielder may decide to cut their losses and teleport away if the situation becomes too hairy.
If the trapped player has no defensive spells or skills to deal with staying put, they can still strategically take the damage which they can then try to mitigate in other ways. The caster can't force them to stay put, but they DO deal a small amount of easy damage (without being able to destroy their helpless opponent as is currently the case--paper cuts instead of napalm).
Players that are prepared to stay inside Prison and defend can grow their mana advantage every time Prison is cast on them if they are successful...but are giving their opponent an opportunity to exploit their hesitation to move.
Practically speaking, the primary strategy for Prison would change and become more about the caster trying to force a Teleport to do damage by threatening with other spells (not typically actually doing damage with those spells). The castee, of course, is trying to NOT teleport so as to waste their opponent's mana.
Being able to tune the damage (in addition to the cost and duration) would make it a lot easier to fine tune the balance of this spell.