How do pet effects work? (3 pets)

i have seen that certain pets, like ruby or the dragons, have an effect when you have 3 pets out, i was wondering, how do these effects work? basically my questions:

-what combination of pets get effects?
-can you turn the effects on/off, or if you have 3 pets that can make a combination, they will always have it going?
-anyone has pictures of what the effect look like?

so far i have seen the 3 dragons (summon a huge ice dragon)
3 myr/ruby (summon hearts of theyr respective colors with the dragon symbol)
3 robo pets (some weird HUD with the guy from omega sector)

i am mostly interested in question number 2, since a friend wants to get a third white tiger, and says the effect is hideous.