You can use this card with an "Injection Fairy Lily" to increase her ATK to 3000 during one turn, which can then be further boosted to 6000 using her effect during the Damage Step.
This can form an OTK with Megamorph, as Lily's effect of paying life points increases your chances of having fewer Life Points.
Target a Level 2 Spellcaster with this effect, then Synchro Summon "Junk Warrior" to give it a 3000 ATK boost. This is sufficient for an OTK, because "Junk Warrior" is not a Spellcaster and will still be able to attack.
This card works rather well in a Fortune Lady deck. The Fortune Ladies can swarm with ease thanks to Fortune Lady Light, and they normally have low attack scores when they first hit the field. If you use this card with Fortune Lady Dark, you are more likely to Special Summon from your Graveyard a Fortune Lady.
After increasing the ATK of one of your spellcasters with this card release the other spellcaster for the summon of a non-spellcaster or as cost i.e. for Enemy Controller.
This card works well with Magical Exemplar. The Exemplar calls for a second spellcaster (with a strong effect). Then Magicians Unite increases the ATK of the new monster (eventually twice if the new monster gains spell counters/ATK for every used spell, like Mythical Beast Cerberus).