Why you should run the Serpent Lantern adventure pack
Serpent Lantern and the day of tomorrow
Serpent Lantern is one of the older adventure packs in Champions online. In the old days, an adventure pack represented an instanced dungeon with a storyline and special drops from the creatures inside, which you had to pay Cryptic Points for to acquire. Without buying it, you couldn't run the adventure and you could only get your hands on some of the items that dropped there via the Auction Exchange.
With the recent On Alert patch, several things in the game have changed, one of which being that all adventure packs are free. This includes Serpent Lantern, Demonflame, Aftershock, Resistance and Whiteout. The last three provide especially nice goodies, so question is why you would run an older adventure pack like Serpent Lantern?
Glad you asked - keep reading to find out.
Serpent Lantern Trailer
The Question of Questionite
Questionite is an important currency; you can use it to buy items in the Questionite Store and even convert it into Cryptic Points via an Exchange. One of the quickest ways to gain it is via the Alert dailies provided in Rennaissance Center - but it's not necessarily the best way. Completing the entire Serpent Lantern Adventure pack gains you 2000 Questionite, while each of the bosses inside (Viper X, Freon, Draconis, Lady Viperia and the Spirit Serpent) has a chance to drop a Box of Questionite, good for 200-1500 Questionite.
This means that your total haul for Serpent Lantern is 2000-9500 Questionite. And with each of the bunker-busting missions, Serpentia and the Spirit Serpent representing piecemeal chunks of playtime, you can spread it out between Alerts and quests.
There are several costume pieces that can be acquired from this Adventure Pack. Each of these can be used to gain a costume piece for use at the Tailor for yourself or your Nemesis characters. In addition, once you have completed Serpent Lantern at least once, you can also use Questionite to purchase the costume unlocks and action figures from the Questionite Store (note that these are the same as dropped by the Serpent Mages in most cases).
None of the minibosses themselves drop costume unlocks.
The following items (in brackets) have a chance to drop from the Serpent Mages (16 total in the Adventure Pack), and can also be purchased from the Questionite Store under "UNTIL items". These items are Bind on Equip, and thus can be traded or sold on the Auction Exchange.
[Serpent Lantern Belt] Viper Belt
[Serpent Lantern Boots] Armor Viper (Feet)
[Serpent Lantern Bracers] Armor Viper
[Serpent Lantern Emblem] Viper Logo (Emblem Front)
[Serpent Lantern Emblem 2] Viper Logo Large
[Serpent Lantern Full Mask] Viper Logo (Full Mask Pattern Cloth)
[Serpent Lantern Full Mask 2] Viper Logo (Full Mask Pattern Leather)
[Serpent Lantern Full Mask 3] Viper Logo (Full Mask Pattern Metal)
[Serpent Lantern Helmet] Serpent Helmet
[Serpent Lantern Hip Armor] Subligar: Viper Long
[Serpent Lantern Mouth] Armored Serpent Jaw
[Serpent Lantern Shoulder Pads] Armor Viper (Shoulder Pads)
Double Loot Day
While an unintended bug (most likely), the bunker mini bosses (Freon and Draconis at least) will drop loot twice when defeated. They often drop blue-quality items with upgrade sockets in them, as well as Recognition and a Box of Questionite. As each box can contain 200-1500 Questionite, this effectively doubles the reward you received to 400-3000 per boss, potentially.
Challenge and reward
Before entering an Adventure Pack's instance, you can select the difficulty you want to run the adventure in. To do this, right-click your character portrait and choose a difficulty level. Personally, I recommend the following guidelines:
Novice player: Normal
Lower-level character with self-healing: Hard to very hard
Any character without self-healing: Hard, unless you do exceptional damage or are a tank
Tank with self-healing and heirloom gear: Up to Elite
These are just recommendations of course, as you practice more and you have more cooldowns or abilities on your character the adventure will become easier to run. Higher difficulty increases the drop chance for costume unlocks, but as of yet seems to have no effect (anymore) on the drop rate of blue/purple items or Recognition. This is likely an oversight which will be corrected in the future.