Learn About Grappling First
Before you do anything else as a DM, learn the grappling rulesgrappling rules. You can find some additional resources provided by Wizards of the Coast here:
- All About Grappling (Part One)All About Grappling (Part One)
- All About Grappling (Part Two)All About Grappling (Part Two)
- All About Grappling (Part Three)All About Grappling (Part Three)
- All About Grappling (Part Four)All About Grappling (Part Four)
Some things of interest to learn so you know what can be possibly exploited (before your players start doing them to your NPC's) can be found in the Grappling Handbook.
**Specific Answers to Your Three Questions**
- Crushing a character to death would be bludgeoning damage as part of a successful grapple checkgrapple check.
- Choking a character to death, specifically, would be a 3rd Edition feat called Chokehold1, a special ability of Reaping Maulers called Sleeper Hold2, or a special ability of Black Blood Cultists called Stranglehold3.
- You determine DC's of things like that (you really shouldn't be thinking of DC's for things like that) by basing them on something readily found in the rules and making a slight modification to suit the situation. That sort of information of how to do that is outlined in the Dungeon Master's Guide. If you are new to DM'ing, I highly recommend reading the entire thing first. Especially since you don't understand all the combat rules in the Player's Handbook.
1If you pin your opponent while grappling and maintain the pin for 1 full round, at the end of the round your opponent must make a Fortitude saving throw (DC 10 + 1/2 your level + your Wisdom modifier). If the saving throw fails, your opponent falls unconscious for 1d3 rounds.
2At 3rd level, a reaping mauler learns how to render an opponent unconscious with pressure. If the character pins his opponent while grappling and maintains the pin for 1 full round, the opponent must make a Fortitude save (DC 10 + the reaping mauler's class level + the reaping mauler's Wis modifier) at the end of the round or fall unconscious for 1d3 rounds. A creature with no discernible anatomy has immunity to this effect.
3At 5th level, you learn to snap the necks of fallen enemies, allowing you to administer a coup de grace with your bite attack as a move action.