I am a Huntress but there's a Monk Guardian that just came up costing 15 Million, has decent stats and 38 possible Upgrades, I was wondering if I could use that on my Huntress or if I would have to get a Monk in order to use it?
[PSN - Volkamar] My MNR Creations - http://www.modnationonline.com/profile/742-volkamar
You can use any of the pets yes. Except the demon imp does not restore health to the huntress traps, only to towers/auras.
Better off with a ranged DPS pet for the huntress IMHO though, that has a different element than your main attack if you have any. Or instead ranged pet with very high knockback that keeps enemies off you. Or a hawk/tiger with high damage who doesn't need as much knockback, but only works on enemies that are pretty close to you. Which the melee pet can work well, especially with the flamethrower and trap specialty.
The guardians only work on one trap/tower at a time, the guardian chooses basically at random which one to buff. Usually the trap/tower that is closest to you which is oftentimes not beneficial at all. The rest of the traps in the pets range do get boosted, but it is extremely minor and not enough that would ever make any difference.
If anything you might want the huntress guardian pet which increases trap reset time or possibly the apprentice one who increases tower damage (however her traps do so much damage, they don't really need a boost). Increase of trap area of effect is not worth losing out on thousands of DPS of a dragon/chinese dragon/gryphon pet.
That and you're better off farming the last boss for a good guardian pet rather than buy one in the shop for that much mana, with the higher difficulties giving you better *chance* of a better pet.
Oh I forgot about the Genie. Well it depends. If you're built for hero damage, sure since it gives mana based on your damage. It doesn't do any damage itself.
Invisibility doesn't need extra mana really. Just helps with piercing shot basically.
If you have a bone bow (which naturally pierces enemies), grenade launcher, flamethrower, or ray gun then piercing shot isn't really all that necessary. And most probably won't give you equivalent damage of a ranged DPS pet even with another kind of weapon.
You could walk around with constant invisibility, but you already can since enemies drop ridiculous amounts of mana and you don't need many points in invisibility to get it to 1 mana per second cost.
For the portal gun, it would probably be the best choice though. Almost forgot about that gun.
That's just my opinion, I'm sure whatever pet you choose you can make to work for you.