I have read several times in the forum that mandalas should not be boosted.
but I want to try; I would like to know how I should place the “michael or thor” image, depending on the case, how should place the image face down or normal face up image on the sigil?
Either will work. I prefer face up since the sigil is face up.
good argument 
Have you ever boosted a mandala?
I can’t remember. I think I boosted a higher self mandala once. It’s hard to remember everything. Boosted a few tags for sure.
Boost “Smilodon Bones”?
Please don’t. That thing is Apex Predator enough for a literal actual gangster.
what would be the best way to boost ; boost mandala that already used in a necklace or boost a new mandala
Fields on Mandalas grow stronger over time so if you are aiming at maximum strength boost the ones you’ve had for a while. But if you don’t want to risk ending up with something too powerful where you would rather you had the originals back, try out boosting some new ones first.
thank you