I was going to ask a very similar question in a context of speed-running Dawnport, which leaves you with a surplus 8-level characters in the process. How one may extract wealth with minimum time investment before deleting them?
@Williams already provided most of the profitable endeavors, so this answer should be considered as addendum.
General Hints
Use features available only for beginners (usually up to level 10), to save time on characters' slow movement.
- You can insta-travel between cities for free with the help of Charos in the Adventurer's Guild (up to 6 times according to TibiaWiki).
- Every ship's guide NPC will teleport you to a corresponding depot.
- Use a time ring to boost your moving speed for 25% in cities; 20% on grass, gravel, heavy and medium dirt; 15% on light dirt/sand/snow. (See speed 138 row here)
Receiving rare items
From a speed running perspective, logout block is the archenemy of profit and fun. For instance, considering the cases brought by @Williams:
- Getting a Diapason from NPC Edala requires ~1 minute to reach her, 7 times of 10 seconds to perform login - use lyre - say hi - switch character sequence, and another minute to go back to the depot.
- It is way harder to quickly rotate characters in order to dig a Leech.
Possibilities not mentioned previously:
- (FACC) Noodles is Gone Mini World Change to get a Fan Doll of Queen Eloise. This is similar to the Rottin Wood's task, but it scales well with the number of your characters. The trick is to find Noodles with your main character and then push him all the way to the castle (say hi to stop him from strolling). Then you can quickly do the quest within ~30 seconds per character. There is ~1% change to get the item and it is worth up to 1kk on some servers.
- (PACC) Open Blessed Wooden Stakes manufacture. This quest require about half an hour to set up per character and works best if you don't want to offline-train them so they can stay at Chondur's hut. The trick is that if you have a bunch of wooden stakes, you'll have to hide all but one in his furniture.
- (PACC) Each character can get one Elvenhair Rope (10-50k) from the Troll Sabotage Quest. You'll need to lend each character BoH + Helmet of the Deep. It takes a few minutes; just don't do it in nighttime (were-creatures).
- (Dawnport/Rook before leaving) This was a surprise to me, but Legion Helmets are rares now and people pay 10-50k for it. They can be easily obtained in a quest before leaving for the mainland. You'll just need a pick.
Seasonal:
- (PACC) Hot Cuisine Quest requires a 35 lvl character, therefore a lot more effort (at least a few hours). However, the gain is huge with about 5kk when doing the quest for the first time (i.e., cooking two times). Moreover, it has a synergy with a boss-checker use-case (see below).
- (FACC*) During The Lightbearer event (November 11th–15th) you can get 20x Midnight Shards worth in total ~300-500k per character (or you can spend them to raise the char level from 8 to 17). All you need to do is to safely rotate the characters to light the basin in Dwacatra. * – you need to obtain the Magical Torch.
- (PACC) During the "a Piece of Cake" event (February 21st–26th), multiple hungry characters are useful to eat through the cake bridge. Once the main quest is done and a bit of walking around, you will obtain one of the cupcakes – with prices of some of them oscillating around 1kk.
- (FACC) This is slightly less profitable and requires another char to AFK. During The Colours of Magic (March 15th–23rd and September 15th–23rd) collect 1 powder of color A and 20 of color B. Have the AFK player to use the A-colored powder, and rotate the chars each tagging them with color B. You'll get a Zaoan Chess Box once, and extra yearly changes to obtain the queen. The easiest way to get a lot of powder quickly is probably to visit a big penguin/bat spawn.
Other uses
Apart from monetary gain, such characters may be used to save time and effort on your main character(s):
- Have a character next to The World Board in the Adventurer's Guild to quickly check for today's Mini World Changes. Additional characters may be used to, for instance, narrow the location of Yasir.
- You can offload your limits on the market (100 offers) or depot (2000 for FACC).
However, the most prominent use of extra character is to check for boss respawn which often requires them to survive in harsh conditions. This require a lot more of time involvement.
Leveling up a knight
Knights are arguably the easiest to power-exp from level 8, because they are the least restricted with DPS. After offline training them to 60-70 axe skill and equipping them with a Ripper Lance (28 atk, lvl 0) they will deal ~85 dmg on average, single-hit killing a Larva most of the time. Because over-leveled knight weapons just lose 1 atk/def point per missing level, after reaching character level 14, your best weapon (until lvl 29) will be a Naginata or an Ogre Choppa (39 atk, lvl 25), and the character will see a boost of ~3.5 dmg per level without leaving the hunting location.
Source: own research + the linked TibiaWiki articles + the Formulae article. I will update the answer if have new ideas.