[Kromm]

It has several drawbacks in actual play, but most important, it's Resisted by HT.

On the monster's side of the resistance roll, monsters typically have decent HT. Many have Magic Resistance, which adds to this.

On your side, there's the -1 per yard to cast a Regular spell such as this one (Spells, p. 12). With a three-second casting time, and your movement during a Concentrate maneuver limited to a step (Exploits, p. 31), you have no guarantee that a subject who isn't limited to a step won't have moved very far away – giving a large penalty to cast – when you finally get to cast the spell. If the monster has Magic Resistance, it penalizes you as well. And then there's The Rule of 16 (Exploits, p. 8) to cap your skill.

Whether or not the monster resists, you still pay the energy cost (Spells, p. 14). This is 10 energy . . . for an SM 0 monster. Many monsters are SM +1 or larger, making the cost 20, 30, 40, or more energy points due to the multiplier for SM on the cost of Regular spells (Spells, p. 12). That is substantial.

In practice, you won't be casting with any guarantee of success. If you blow it, you have to concentrate for another few seconds. And you'll be paying a lot of energy for your effort.

(Plus of course the Suspended Animation angle isn't useful if your target has Doesn't Sleep, which means Entombment is basically "anger a monster and bury it for a while." Most things with Doesn't Sleep also have Doesn't Breathe and Doesn't Eat and Drink, so they won't just suffocate or starve. It could backfire spectacularly.)

All told, it's balanced by all the ways it could go wrong.