If I already have one then I wait to see if there are better moves in the future. I have a maxed out Salamence with near perfect stats but have a 100 IV waiting on a community day move. If it turns out that a future move is not worth it then I don't have to evolve it during the event. If Draco meteor becomes legacy then I at least have one. Draco meteor isn't my favorite move because of it being one bar anyway. It's a case by case decision.
GamePress
New "Legacy Move" candidates
I have a couple 'mons that I could evolve, but waiting for either a) a better one, or b) enough candies to actually power it up after evolving. Most notable one is Bagon (current best is 89% lvl 20, only candy to get it to lvl 22.5 after evolving w/o using rare). By waiting, am I running a risk of losing it's best moveset when they roll out gen 4? Are there any with a crappy move pool that people *should* wait on if they have less than ideal candidates in case a better move comes? Thoughts in general about legacy moves?
