my lightning reaches its destination and the monster has moved, it simply stays put, not dying. The way I tried to go about this was something like "If move-to destination reached and no Monster collision detected, then destroy lightning" but it doesn't seem to activate...
Please show the event you made for this.
For the second event from looking I think you filtered the instances down to the one the lightning is overlapping then tried to pick all again. If it's a sub event you can open the picking again with pick all instances first then add the logic pick a random instance where UID is eclair variable.