Some efficient ways of leveling 20 characters at once (Horde side)?

[nodoze]

I thought about doing that, but I had some concerns that the strategy of pulling the entire dungeon and then leaving the party/instance might be considered abuse and be bannable. Is it the case?

If you mean having main(s) leave the raid and then converting the remaining alts to a party and using mains before you are auto-teleported, yes that is bannable.

In hindsight the fastest way to get 20 characters to cap (assuming you don't have 4 5man AoE teams) likely would have been to take a hunter team to cap and then use their pets to power level...

The following thread covers the options:

https://www.dual-boxing.com/threads/...summary-thread

In your situation the following stand out to me as options to consider:

Leverage 'Approach 1' by using 1 level 60 main to boost 4 low level alts at a time and leverage average team levels in dungeons. My main Paladin is in his 50s and once I get to 60 I plan to use him to boost 4 AoE alts that are in their 20s. In this approach your main and your 4 alts are in the same party in the dungeon.

Leverage 'Approach 2B' in the open world you can tag with a low level team (2+ alts per team) and kill with pets if the mobs are not green to your main(s). In this approach you main(s) and alts are in separate parties...

Leverage 'Approach 2A' in the open world you can tag with a lower level alt/team and kill with the mains if the mobs are green to your main(s). In this approach you main(s) and alts are also in separate parties...

Note that those last 2 are likely not very viable on PVP servers right now.

Edit: Denoted which recommendations follow which Approach delineated in the Power Leveling thread...