Enter field W1 (the first field of the game) in Journey mode and without any battle traits.
Salvage any gems pre-placed on the field, then place a tower directly above the Orb of Presence and insert a gem of your choice into it.
Start all waves and thin them out, preferably to a single monster. Drop your gem to the inventory and let the monster get banished by the orb several times (this will also most likely give you the "Teleport Lag" achievement).
After a few banishments, click on the monster and see how much mana it takes to banish. If the banishment cost is considerably above your current mana, then place the gem back into the tower above the Orb, reduce its range (using the scroll wheel) to a percentage that covers just a little past the orb. Wait for the monster to approach the orb and then the shot should blink to the monster, killing it, and giving you the achievement.