Due to the very nature of the fact that these are "improvisational" stunts, this set of rules is really more of a guideline. Sometimes players will come up with stuff that doesn't necessarily fit well into this framework, but hopefully it provides a solid enough framework for GMs to build off of and adjudicate fairly.
THE BASIC IDEA
A Gamble is whatever the player would like to achieve. The options below should cover a wide variety of possibilities, with the mechanics reflecting the intent of the action. The intended effect can be described in whatever narrative way that the player sees fit.
Gambles are usually a quick action skill check, but some of the more impressive effects require a standard action.
Risks are consequences chosen by the GM. If the skill check for the Gamble fails, then the Risk is triggered.
Any quick action Gamble can be used as a standard action to avoid a Risk.
The DC for skill checks will either be based on the standard difficulty for the environment, or if the action directly opposes an opponent then their PD or MD is used instead. For simplicity, targeting PD or MD is equivalent to a Normal difficulty. If the action would normally be a Hard difficulty, add 5 to PD/MD.
Combat Maneuver (quick action): Make a skill check (usually Str or Dex) against your opponents PD (usually). Optional - stronger effects may additionally require you to hit with your next attack this turn, or may be triggered with a natural 16+ roll on the skill check.
Trip - The target is Stuck until they spend a move action to stand up. Optional stronger effect - melee attacks get a +2 bonus to hit the target.
Bull Rush - The target is pushed back a few feet, popping them free of any engagements except the bull rusher (and potentially pushing them into new engagements) Optional - if pushing the target into dangerous terrain (a fire, off of a cliff, etc.) you have two options. You can use PD + 5 as the DC (or a Hard DC), or you can allow the target a Normal Save to negate the effect. I prefer increasing the DC personally, because it minimizes die rolling and speeds things along. If the target is Large or Huge, add an additional +5 to the DC (so it's Very Hard to push a larger creature into dangerous terrain).
Grapple - The target takes a -2 penalty to disengage checks (you must have at least one hand free).
Gain the Advantage (quick action): Make a skill check against the target's MD or PD, or use the Normal DC for the environment. Choose 1 of the following effects (or similar), which lasts until the end of your next turn:
- the target is Vulnerable
- you or 1 ally gains a +2 bonus to attack rolls against the target
- you or 1 ally gains a bonus to damage against the target equal to your level.
Optional - double the bonus on a natural 16+.
Players that really like to gamble may want a stronger effect. Feel free to give it to them, with a Hard DC (or adding +5 to PD/MD). Instead, they may choose from these effects:
- the target is Dazed
- the target is Hampered
- choose one of the Normal DC effects, and make it Save Ends.
Examples: Anything that falls into the umbrella of an Agility or Smarts trick in Savage Worlds probably works here. Taunting the opponent, throwing sand in his eyes, feinting, using footwork to improve your relative positioning, etc.
Massive Attack (standard action): First, make a skill check (Hard DC) with an ability appropriate to the action you're describing. If successful, you can make a basic attack against 1d3 nearby enemies in a group (whether it's a melee or ranged attack depends on how you describe the action).
Examples: Sweep attack, cutting/shooting the rope of a chandelier, throwing a table, etc.
Increase Momentum (standard action): First, describe how you're increasing the momentum of the battle and then roll a skill check with an appropriate ability (Normal DC). Immediately raise the escalation die by 1 on a success. This should probably be limited to 1 attempt per battle, but if you're feeling generous you should at least require a different narrative description for additional attempts (in other words, momentum gained from the same description doesn't stack).
Reversal: One enemy (usually the target, but a ranged leader or lurker works well too) makes an immediate basic attack against the character. If it makes more sense that the action would endanger an ally, then an ally can suffer the reversal (this will usually only happen if the character that took the Gamble is in a fairly safe position).
Vulnerable: Until the end of the battle, the character is Vulnerable (+2 crit range to all attacks targeting the character).
Lost Momentum: Decrease the escalation die by 1. This should usually be a pretty dramatic event, so you shouldn't overuse it (in other words, don't do it more than once per battle, but see Increase Momentum).
Backfired: Something went wrong, and now the character is either Dazed or Stuck (save ends).