It's an attack where the person will always do a critical attack, even the final bosses that have the Mantle Skill. It can be done with the three brothers (Rolf, Boyd, and Oscar), as long as they all are equipped with bows (you'll need to promote Oscar to do this, because he can't use bows as a Lance Paladin). They'll have to be positioned like this:
o
o x o
X is the enemy, and O is the brothers. The position can be rotated, but it'll still be in a triangle shape, thus the name of the Triangle Attack. The pegasi (plural for pegasus, not pegasusES) knights can also do this (Marcia, Tanith, Sigrun, Queen Elincia) and be positioned like this:
0
0x0
To me, doing the Triangle Attack with the 3 brothers is better, since they all are in different classes, while the "pegaseses" knights are all the same class. This wouldn't have been too much of a problem except that the P.K.s all have weaknesses to arrows and wind magic. But personally, doing it with the P.K.s would be easier in my opinion.
I hope this helps you out, as I'm doing this instead of my school work right now. If you have any more questions, message Andrew Heo on Facebook.
...I sure hope you're not a creeper.
You can't. There are no cheats in Fire Emblem Radiant Dawn.
No, Radiant Dawn is only for the Wii.
in a store...
Yes, there are.
No she died in Fire Emblem Path of Radience
Oliver
I think not.
It already has been.
About 20
No.
As of now, you cannot.
no