I'm not afraid of many things in magic. Mirror matches come close, but only because they are boring.
I say that because I've tried to utilize
Sunbond, multiple times in a myriad of decks embracing counters and lifegain. At 4 CMC, the enchantment is slow, and is far to situation dependent for its strength. It got pushed out of
UB Peck of Life because there was always another card I wanted to play turn 4.
Hero of Iroas makes more efficient, but at that point you're crowding out your abilities to gain life.
I've play tested
Sunbond as mono color, and even every dual and tri combination. It is a turn slow, and far to dependent. Works as filler for a Commander deck though.
So, what have you been beating with this?