Tri-fusion? :o

I'm interested in Tri-Fusion but I have no clue how it works. Does everyone get the same demon?

Well, no, only the player who "hosts" the Trifusion gets his demon. The others who partecipate "sacrifice" their demons, that's why you can give them some rewards.
You can make common demons by trifusion, or special ones.
Some of them may need a plugin, a special item or quest that permits you to fuse it. Some of these plugins require AP items, others just need to accomplish a quest, defeat a field boss, or collecting some items.
Then we have some special trifusion demons that do not require plugins.
Here's a list of Tri-fusion demons that don't need plugins:

lv 42 - Thoth
lv 70 - Odin
lv 74 - Mithra
lv 58 - Dionysus
lv 40 - King Frost
lv 59 - Hecate
lv 64 - Moloch
lv 69 - Loki


Here's a list of Tri-fusion demons that require NON-AP plugins:

lv 92 - Lilith
lv 85 - Mot
lv 93 - Beiji Weng
lv 76 - Thor
lv 82 - Hecatonchires
lv 76 - Pallas Athena
lv 80 - Uriel
lv 93 - Raphael
lv 86 - Nyaralathotep
lv 93 - Wu Kong
lv 77 - Qing-Long
lv 93 - Phantom
lv 72 - Bishamonten
lv 72 - Surt

To acquire some of these plugins, you need to complete your acts in a certain way, as well as an alignment chose. So, if you're interested in any of them, you'd better check out before completing story acts

And here's a list of AP-Plugin Demons. You need Hacked-Chip Alpha and/or Essences of Yetzirah in a certain quantity to obtain them.

lv 20 - Lilim the Little Demon
lv 30 - Matador
lv 35 - Alice
lv 46 - Hell Biker
lv 70 - Girimekhala
lv 95 - Mara

Hmmout of all of them the only major one i would want is Thor