Singleplayer session:

Version used : Pixelmon-1.12.2-7.0.5-universal
forge-1.12.2-14.23.5.2768-universal

Problem: When battling a wild pokemon or trainer , either your own pokemon or the enemy pokemon can actually move the player when battling (attack animations). This can result in falling into bottomless pits , lava, or from a cliff. This is even more problematic when in Ultra space , Nether and The end for the sheer quantity of bottomless pits and lava included in these areas.

Suggestion: Make it so when you call the battle start event that it disable player collision entirely until battle end is called.

Thanks for the report. I'm not entirely sure as to whether this is a bug (or whether making players immovable would break anything), but I'll pass it along. Keep an eye on the ticket to see what's up!