Travelling in time.

Mogmush stared at the mountain. he knew that within the huge iron and granite doors all sorts of vile and generally grim deeds were being committed. He had seen the monsters and their feasts and something other than booze was burning away in his stomach. it felt a lot like anger.

"Your're th' wizard! Open the bloody doors!"

Mogmush leered at Gudguff the wizard and jabbed a meaty finger at the portal before them. Behind them the trees bent under the caress of a gale. The Wizard looked quizzically at the barbarian and conveyed, in one simple and yet encompassing gesture that he hadn't heard the...request... and also that he was indeed a Wizard and was owed the respect of his title. 

"I said! Open the doors!" Mogmush jabbed his finger toward the door again and spoke in the slow and clear tones of a man dealing with a simpleton.

Gudguff frowned at the barbarian. 

"You do realise that those doors are three feet of iron over twelve feet of granite." He stepped forward and swung his staff gently at the gates. The staff cracked and snapped backwards at a hundred times the speed. Gudguff held the splintered and smoking ruin of the staff before his eyes and examined the shards of wood sticking out of it. 
"It's also protected by as vicious a rebounding enchantment as I have ever seen." He eyed the faintly glowing runes that were slowly fading. "In fact this might be unique. I don't think I have seen anything as powerful as this since the golden age of sorcery."

There was a long pause as Mogmush seemed to absorb most of what he had been told. 

"So open it then."

There was another long pause as Gudguff went through several unhealthy shades of skin colour before he gave a measured and appropriate response. 

"What part of this don't you understand you hair brained cretin!? It's ridiculous! The only spells that could get through it died with Anathrom the Black! He's been dead a thousand years and then some you tit! I can't do it! He probably couldn't have done it!" The Wizard wound down as the wind gently whipped some of the froth away from his mouth. Mogmush nodded and took a swig from the flask of brandy he'd picked up in the last town.

"So learn?" He belched slightly and wandered off to find some stones. The rebounding spell might be good for a laugh while he waited. 

"Learn!? Learn!?" The Wizard's face started to change colour again before he pulled his pointy hat off and started to gnaw on the rim. Half way round he stopped, an idea forming in his overworked mind.
"Learn..." 
                                                                              ***
Mogmush returned from the edge of the trees with a dozen decent sized stones. He was risking immodesty by carrying them in his loincloth. He figured it didn't matter as he was up in the mountains, several squirrels would have argued but they couldn't quite work out how to convey their embarrassment and settled for chattering at the huge man from a nearby tree.

"What are you doing?" Mogmush asked the Wizard. 

Gudguff was standing in a circle made out of bits of sticks and surrounded by runes gouged into the shallow earth. 

The Wizard looked up at the massive barbarian and grinned a manic grin. 

"I'm going to learn!" 

Mogmush looked on as the Wizard uttered some mystic runes and waved his hands in gestures that caused strange patterns in the air. Mogmush stared as he sorted his stones into groups. There was a blinding flash and the Wizard dissapeared. 

"Huh." The barbarian patted out the small fire on his loincloth and put out the the flames that were eating away his eyebrows before walking across the scorched earth and gentle knocking on the huge doors.
"Anyone home?" 

Time travel.
Time travel has previously been a preserve belonging to Sci Fi, but why? It fits the Fantasy bill perfectly. It's basically mucking around with the fabric of reality to create a new/better reality, or at least one that meets with your Hero/Wizard's aims.

I get you! Yeah it makes sense, you're making the world work for you!
More or less.
terry Pratchett is a prime authorial example of some one who has used time travel, several times, to great effect. It allows him to mess around with his established universe without messing up any future plot lines and without ruining his universe. It's a bit like the "It's all a dream" set-up but without the cringing horror or wasting your reader's time by having a plot which actually doesn't matter.

Riiight...soo...
So, example time!

• Situation-The Dark Lord Sorebum is winning and things are looking seriously hopeless. 
• The Wizard council or conclave or whatever they are realise that their hero has been converted to the Dark Lord's legions and is now wearing the spiky and dark uniform of a baaad dude.
• The Wizards are now so up shit creek that they decide to send one of their members back in time to try to stop the Dark Lord from converting their precious little hero.
• They desperately race against time and the Dark Lord to create the spell needed and send a wise man back to enact their changes.
• It goes wrong and they send a confused simpleton back who can start a fairly low key resistance.
• The simpleton's mind is scrambled by the spell and he/she ends up as the Dark Lord's most trusted henchman. 
• See point one.

What?
Yeah, that's the problem with time travel, it can sometimes make more of a mess of things than it sorts out. The film Butterfly effect deals with exactly this problem.

Drawbacks
The thing about time travel is that once you'e managed to go back in time there is no telling what your presence and the changes you make will actually do.
Also, once you've gone back in time you have no idea how long you need to be there to effect the changes that you need.
You then run into the problem that the timeline you have come from might actually be the result of you going back there in the first place, in which case once you're back there and you get back towards your original timeframe you might realise that your intended changes have done nothing, and then you might want to try to change something else by going back further and trying to warn yourself (assuming that such an act would not destroy the universe) or to change something further back that might effect you when you go back in the first place. But then you run into the "it's this way because it's this way and it's this way because of what I tried to do to change it" thing.
Often referred to as a paradox, or a thing which can only happen/exist because it has happened/exists. Much like a Dixon's sale, it is there because it is there and there is no time when it isn't there but theoretically it has to end at some point and has to start at some point...I dunno, bad example.

But doesn't make time travel difficult and sort of pointless?
Well more or less, yes. The major problem with time travel is that it actually ties your head in knots. The human mind perceives time in a linear fashion, like a road. We do this for good reason, namely it hurting to do otherwise. Also, given we evolved from primates mucking around with concepts like "I ate the banana in the morning so I am hungry in the evening" is probably not a good idea. I.E. "I ate a banana in the morning and is evening now but I traveled back to this morning to eat the same banana before I ate it the first time round and now I'm twice as hungry and also wondering what happened to banana I ate the first time round as I can't feel it in my stomach anymore."

But, to give you a simpler example of what might happen...


Mogmush stirred and slowly woke up, struggling and kicking his way out of his blankets. He grunted as he let a stream of piss fall into the ashes of his campfire. 
Mogmush was thrown onto his back as a crackling sphere of lightning appeared roughly where the wizard had disappeared the night before. 

"Ow..."
Mogmush stared through the protective circle of his arms. In the centre of the dissipating sphere Wizard Gudguff lurked. He was robed in black and carried an enormous staff. It looked like it was engraved obsidian and it was topped with a small skull that had more eye holes than Mogmush was comfortable. 

The Wizards gently glowing eyes swiveled around and glared at Mogmush. 
"What day is it?" The Wizard's voice held tones and undertones that caused the air to vibrate in strange ways.

"Tomorrow?" Mogmush hazarded a guess. 

There was a loaded pause as the Wizard looked at the Barbarian and frowned.

"Bugger." The word shattered the otherwise imposing image that the Wizard had been going for and he deflated a bit. "Fine. Lets get it over with."

Mogmush lurched to his feet and stood a respectful distance away from the Wizard.

"I take it you learned then?"

"I studied with Anathrom the Black. To do this I had to prove myself by venturing into the unfromed lands and battle with a greater demon. I had to forge a staff from the soul of a volcano and inscribed it with the runes of power which I had to steal from..." Gudguff took in the slightly glazed look on the Barbarian's face. "Yes. I learned." He sighed to himself and for a moment found himself wishing to be back on the demon haunted plains of the unfinished lands. 
"You might want to stand back."

Mogmush stepped back and looked on as the Wizard seemed to do nothing. Gudguff breathed in and uttered a single, soft word. 

Mogmush felt his loincloth fluttering as a vacuum formed around the Wizard. A thousand square yards of air was being compressed into a space about the size of a pin's head in front of the Wizard. Gudguff spoke another soft word and glared at the huge stone doors. His hair seemed to crackle and the energy was suddenly released. 

The oxygen in the tiny space was set alight with a word of power and a tiny star was born. Gudguff flicked his fingers toward the doors and tiny flare shot forwards and ploughed through the rock and the iron like a hot knife through warm butter.

Afterwards, when Mogmush had stopped dodging the falling stone chips and molten iron shards he looked at the place where the door had been. 
What had been the front of a mountain was now a gaping black hole. The rocks were glowing and dripping slowly as the intense heat slowly dissipated. On the other side of the doors were the incinerated remains of both the monsters and the victims they had been there to rescue. Gudguff was wandering amongst the ruins and prodding at the odd charred ruin. 

"Weren't we supposed to kill the monsters and save the people?" Mogmush yelled. "I mean, dont get me wrong, the monsters are definitely dead. But so are the people..." 

The Wizard turned around and suddenly Mogmush wasn't sure what he was looking at anymore.

"Let the God's sort them out."