1: GM Intrusion
I always look for a way to add a GM Intrusion. In fact, I often start the combat out with one. This grabs the players attention and usually puts one player character at risk. Most creatures come with GM Intrusion suggestions right there in their descriptions.
For example, if I'm using a travonis ul, I can see the core book has a very nice GM Intrusion: a character is overwhelmed by a flurry of tendrils and becomes lost under the massive creature. Each round the character automatically takes 10 points of damage as they are crushed into the drit. A Might task will free them. I'm pretty sure I've got that player's attention.
It's so easy to create your own creatures in Numenera, and here are some ideas for designing GM Intrusions tailored to your own creatures.
Other GM Intrusions may occur to you. An explosive cypher may kick back bits of twisted metal from a ruin as shrapnel. The floor can cave in. Another travonis ul can show up. Gravity could reverse. All of the above!
The core book has lots of great advice on GM Intrusions. Want more? I recommend Taking the Narrative by the Tail: GM Intrusions and Special Effects. It's 99 cents, so go ahead and splurge.
2: End With a Bang
If combat is looking to go longer than about 3 rounds or so (I look around the table and look for flagging interest), I change things up to End With a Bang.
Here's what I say about nasty opponents when I want the combat to finish soon:
The big beast with mouths on its claws roars and charges, disregarding its own safety in an attempt to finish you off. Its Speed defense drops one level, but if it hits you, you're going to be hit hard.
Then I add the creatures level to it's damage. I wing it if adding the level feels too hard or too easy.
For minor creatures, like minions or packs of lesser creatures, I say:
The little squirmy guys back away from the big beast, seemingly shaken by its mad rage. Their Speed defense drops one level, and they won't hit any harder than before.
The PCs will hit more often, and really want to spend effort to avoid the "boss monster's" attacks. The little guys might flee once the big guy goes down.
Enjoy! I'm sure you'll find your own techniques. Like anything else, the best way to learn to be a great Numenera GM is to do it.
PS: Most combats in Numenera are over before they get old, so you may never need my End With a Bang idea.
However, I'm the kind of GM who really likes to challenge my players, so I throw terrible foes at them. They say they can tell if I'm running other people's adventures because the creature levels are "so low." Usually with the right cyphers, effort, and die rolls, my players find a way.
Sometimes, they don't, and I want to end with a bang. I've explored stealing mechanics from 13th Age to use the Escalation Die and Escalating the creatures, but in reality, I don't do that. It says something about the simplicity of the Cypher System that a very simple rule from the d20 world feels overly complicated when you use it in Numenera.
My End With a Bang is inspired by 13th Age's Escalation die, but feels more Numeneraish.