Triggered Actions

2 claws/1 bite... iconic monster stat-line -- but, what if the bite attack did twice the listed damage and was only triggered if both claws hit? Obviously both claws have to hit the same target, like grappling and hug attacks. 

With if a dragon's breath weapon was only triggered on a critical hit? It would need a greater threat range than just 20, say 18/19-20 (20 would still be double damage.) Their breath weapon becomes an unpredictable bonus attack that occurs after all melee strikes are determined. And if multiple crits are rolled... prepare to burn!  

How about wizards getting a free spell if they score a 20 in combat? -- whether they have one available or not. Makes combat a little more exciting for magic-users. Same goes for spell-casting monsters or any monsters' special ability.

Suppose ghoul paralysis is only triggered on a bite (double listed damage) which in turn is only triggered if both claws hit? Makes paralysis less common, but more fun (it is a death sentence after all.)

The assassin's death strike triggered on a crit...? (Said that before, just saying it again.)

A medusa's gaze... Nobody fights medusas, you see statues, you run! Too fucking dangerous. What if her gaze (that's right, HER gaze, Woketards of the Coast) was triggered on her critical hits and your critical failures? 

Level drain, (the dreaded!)... again, make it triggered; 2 attacks, if both hit, then the classic -- grab you by the throat/kiss you/bite you/suck out your breath, whatever it is, followed by your preferred way to deal with energy drain.

Thieves get a pick-pocket check on a crit (if applicable) or a free back-stab, or a back-flip out of harms way, or hide-in-shadows (even if there aren't any!) They're just cool that way!

You see, crits should do more than just double damage.

How about a free attack if your crit slays? (This idea's certainly not new, but it is to someone.)

Clerics/paladins, when they score a crit vs chaos or undead, they (or their weapon) start(s) to glow with holy light and for the rest of the fight they do double damage (triple if another crit is scored, etc.) Who wouldn't enjoy that? It's bad-ass.

The barbarian's rage should be triggered, not planned -- a berserker can not control themselves! So, triggered by their own crit or a crit against them and then they fucking lose their shit! (They should also become a threat to allies while enraged.) If they want to fight the rage, they must roll under their wisdom score on a d20; same thing to end it. A crit on them also ends it.

Mechanics like this make the game more fun. They'll prompt more combats with monsters we've always avoided, and more combats period. Combat is FUN. It is not a failed state... unless you're a thief. 

The possibilities here are simple and numerous.

Tweak your games thus.