If you put a creature you want to use at a later date in an encounter, how could I save that creature near the end of the battle without sounding cheaty. E.g. The evil mage has only 1 hit point left and gets smacked by a barbarian, but wait he has an immediate interrupt which teleports him away. This gets more complicated if the creature gets surrounded so can't realistically escape.
They should run away along prepared routes when they're bloodied or the fight being lost in their eyes.
Creatures that, rightfully, fear for their lives shouldn't fight "until the last moment." Instead, like most sensible creatures, when the fight becomes a lost cause (when they're bloodied, and/or when 20-30% of the group is down, depending on how loyal they are to the group), they'll try to run away. An intelligent villain will have escape routes prepared, especially one that fits possible unusual movement modes.
Bloodied is important, as it's a clear signifier, provides enough of a buffer to survive an OA or two, and is a time when surrender via intimidate becomes possible.
While there's no real need to provide "real" items for alternative movement modes, including elixirs of flying as part of the treasure may be worthwhile.
Some notes from personal experience:
- Be prepared for this to work exactly once. Players can be remarkably good at dealing with common situations that annoy them.
- Make sure that this counts as a complete encounter win. Escaping villains is fine so long as the players objectives are met.
- Be aware of the healing surge rules for monsters.
- Make sure that your heroes get the normal encounter rewards. They achieved victory, so let them savour it. Withholding loot will just make point 1 occur even faster.
I feel that one of the great strengths of role playing games is the fact that the players can actually influence the story...so let them.
If they manage to kill a character you had plans for, it's ok. The villain is bound to have allies, or minions that could take over. The ghost of the villain might haunt them.
And don't forget that this is D&D - you can always rez a villain if you really want to keep him in the game. It even might give him a reason to target the players specifically in the future.
If you want a character to survive a battle, make sure you plan ahead for it. Don't wait until the middle of the battle to get them out of there.
Think about if from the NPCs point of view. Do they know, or at least suspect, there's going to be a fight at that location? If so, they'll have made arrangements for the possibility of their own survival; what would those arrangements be?
Work out why the NPC is even fighting in the first place, when they could just run away. What do they lose by running? What do the PCs gain? Your players are a lot less likely to feel cheated if they feel like they achieved something major.
Do a mental double-check: If this happened on your favourite TV-show, would you feel cheated? If so, your players certainly will.
It is OK to have an obvious and unstoppable effect retrieve or remove the creature from play, for future use. This would be no different from bringing it back as undead, or it having an "evil twin", or it being some kind of avatar etc.
In 4E, the important features to keep from the PCs winning the battle are:
The players feel they have won a victory. The escaping creature should obviously have suffered a loss, and the plot should move forward accordingly.
Experience and treasure should be awarded as normal for winning the battle or completing that part of the adventure.
That's it. Provided the game moves forward, and you don't "stop time" for some unbelievable cut-scene interaction, all is good in my opinion. However, it is perfectly OK for the bad guy to be doing this as a reaction to hitting zero hit points* - this means in game terms removing the active counter from the board, it doesn't absolutely require a creature death, just a win. PCs may also have abilities that trigger on hitting zero, usually that allow them to recover, escape or continue fighting.
You can also extend this idea into plot - i.e. the PCs have to figure out what to do to really and finally defeat their enemy. For example, I have Mind Flayers as bad guys in my campaign, and when outside their lair they are equipped with one-shot teleport home amulets, taking a Minor action to activate on their turn. These can be stopped with powers that prevent teleporting, or that cause stun.
[*] Caveats: That's a bad guy power, and should be in the stat block, including any restrictions on use. It should be of suitable power level for the adventuring tier, and you should always aim to keep number of NPCs powers down for simplicity. This is hard to do objectively for a "favourite" monster.
It's simple: don't.
I firmly believe that players should be able to do just about anything in a campaign. If they are able to kill the villain, let them. He can try to escape, and you can add some elements that make it a bit easier for him, but if the party can find a way to kill him, let them.
Ensuring that the villain survives at any cost reeks of "deus ex machina", and just gives the impression of sloppy DMing. It may be a little extra work to alter your campaign to fit this, but I've always found it's more fun for both the players and the DM to see what effects the party has on the world, it's ever changing, don't make it set in stone.
Also, for the future, try to have at least rough plans in case something like this happens. Always remember my first rule for DMing: No matter how foolproof the plan, your players will fool it. And this is what I love about DMing, I usually reward players for foiling my plans in especially creative ways.
Follow the example of Hollywood or comic books.
- Send in the mooks instead of getting your hands dirty directly.
- Don't retreat when the bad guy has 1 hp left, retreat when they are brought to half-hp.
- Follow a strategy other than blind fighting. If the bad guy really wants a PC's wizzer ring, don't try to kill him, maybe try to sneak in and swipe it when they are asleep. Maybe try to engage the PCs in a bit of verbal sparring in an attempt to convince the PCs to give the bad guy the gear.
- (if your players won't summarily execute a prisoner) In the middle of combat, throw down weapons and surrender to the PCs. They will (hopefully) either turn him over to the local authorities, which opens the door for him to escape from jail and come back stronger and rested.
The surest way is to make sure the players have a reason not to kill the creature in the first place, even if they are forced to fight it. Some possible scenarios:
- Someone has posted a large bounty, but only if the creature is captured alive and turned over to some authority or organization. The creature can always escape its captivity later, when the PCs are gone.
- The creature carries something the PCs want very badly, but drops it while fleeing. The PCs have to stop pursuing the creature to retrieve the item.
- The creature has information the PCs need (and can't get any other way). They have to keep the creature alive to get that information.
- The PCs think the creature is an ally of theirs (which might or might not be true at the time). They'll be less inclined to kill former allies, at least until they learn why they've been betrayed.
Also, if you really want to have the creature around for later encounters, always have a backup plan in case the creature dies anyway. Making the DM cry is the official pastime of D&D players everywhere, so this will happen from time to time. Be prepared for that. You might arrange for a successor, or else introduce some new enemy that the creature had, knowingly or otherwise, kept at bay. You might even set up an adventure requiring the PCs themselves to raise the creature from the dead (for example, because they still need information it had).