In my custom system, I'm working to build a Brawler class, a martial controller. I've got three main class archetypes, a grappler, a stunner, and a tripper. I've got high-level abilities defined for two, but I can't figure out a good corresponding ability for the tripper.
(My system uses different terms, but I'm using D&D analogues for ease of terminology.)
All classes are 10 levels. To take a class, you first need a [Starter] feat, which grants some core function of that class. All classes have multiple possible starters; these define variants of the class progression, with specific class abilities upgrading that core function. If you have multiple feats for the same class, you can spend some "skill points" (how all non-automatic spells/maneuvers/etc are purchased) to buy those alternate versions. The basic action system is kind of like PF's unchained action system, with three 'actions' per round. A basic weapon attack costs two actions, as would most basic spells.
So, the brawler class I've got, all three starter powers use a single action to initiate their manuever, a roll vs touch AC, basically. If that hits, they spend another action to carry through, grabbing, stunning, or tripping the opponent, using an unarmed damage roll to affect the result. The Grab power deals unarmed damage straight up, the Stun power uses the unarmed damage to add stacking Stunned conditions (each of which cancels one action for the enemy), and the Trip power, beyond the basic knocking-prone, can also throw the enemy spaces away. (Basically, the Brawler rolls, and counts the number the damage exceeds a base, like rolling a 16, exceeding a base of 4 in increments of 5, for 2 bonus effects, stunned conditions or yards thrown, respectively.)
There are three boosts to these powers, at 2nd, 6th, and 10th levels.
2nd level: Grab allows the Brawler to spend martial dice, a per-round secondary combat resource, to oppose escape attempts, rather than costing actions, and they can move with the enemy, slowly. They also get a bonus to other attacks on the held target. Stun and Trip both get the ability to chain that power into another regular attack by spending a single extra action.
6th level: All three powers get the ability to spend martial dice to increase the effect; spending dice grants a double-effect of bonus to the attack AND the damage/effect. Grab, the bonus to attacks vs held targets gets bigger, and it's easier to move a held target. Stun, the interval for more Stunned conditions gets smaller, making it more effective. Trip, the interval for yards thrown gets smaller, meaning they are thrown farther.
10th level: Grab, all attacks on the target are automatic successes, rolling with a high bonus for roll-over-X-for-effect purposes. Stun, if you have Stunned conditions greater than one of their base scores, you can choose to leave them instantly dying instead.
But Trip, I don't know. What's a good, high-level effect for a tripping/throwing power? It should be something built into the power itself, so while Grab, a sustained effect, gets boosts to attacks while it's sustained, the Trip/Throw effect is a one-and-done effect, plus I'd want something more original to it than just bonuses to attacking a prone target. What's something I could add to it?
Also, I'd welcome suggestions for a 5th-rank power for each, since each of these still has an optional rank upgrade that the player can buy into when they want. (And remember, it has to be something built in to the function, as an expansion of that base use, not something added on. For instance, in another version of this post on GitP, I got the suggestion of ripping off a grappled creature's limb, but that doesn't work, because it's not part of the base ability.)