Got a pet you need to level quickly? I put this guide together based on my experience leveling my HERC. Comments and suggestions welcome.
NOTE: This guide assumes you are at least level 40 since all the pet leveling will happing in the cube.
1. Get your pet and get it hatched.
2. Get your pet's loyalty to at least 960.
3. Have at least 20 tickets (or 10 mirage) for the cube.
4. Enter the cube.
5. Your goal is to get to room 4 (Mice Bashing). If you go past room 4, find a way to fail a room or die (last resort town portal) to get back to room 1. Rinse and continue until you reach room 4. Room 4 is called Mice Bashing. Full of a crapload of stones that only have like 20 HP but have a VERY HIGH evasion and are thus difficult to hit.
6. VERY IMPORTANT - Remove all your equipment. If you do not, you will be quite suprised at your equip repair bill!
7. Summon your pet. Put your pet on manual attack (you do not want your pet hitting the mobs as it will likely kill the mob).
8. VERY IMPORTANT - Make sure you keep Summer Sprint up at all times. You want to stay ahead of the mobs.
9. Attack mobs with your fists to create a "train". Mobs are non-aggro until hit. ALWAYS keep moving - I would target the next mob as soon as I started swinging on the current mob. Start slow (like 5 mobs) until you know how many you can handle. They only hit for 8-16 HP each, but it adds up when you have a bunch of them hitting you at once. An HP charm is useful, but not necessary. Once you have the train at the size you want (I was averaging about 15-20 at a time with 2500HP), run to the center of the largest group of stones you can find that you haven't hit yet.
10. Start casting Noxious Cloud (veno AOE) as soon as you stop running. The stones will catch up before it goes off and will quite often interrupt you - spam the spell until it goes off (watch your HP in case you need to pot to survive until spell goes off). Voila! Bunch of dead mobs that give full XP (15) to your pet.
11. Check your HP and get it where you need it for the next round. I could do about 3 runs before I needed to pot/infuse/etc.
12. Rinse and repeat.
13. If you run out of time, you can log out in this room and when you log back in, you will still be there.
NOTE: You can actually get lucky and kill a stone with your bare hands (VENO TANK) so if your Noxious Cloud isn't casting, make sure you have a mob in your train selected (I almost died figuring that one out).
Using this strategy, I was able to level my HERC from 1 to 41 in about 1.5 hours. I didn't use any charms and only a handful of pots (when I got spam interrupted from training too many mobs).
Good luck, and any additional hints/tips are welcome.