Don't forget that this card will activate the last effect of the "/Assault Mode" monster, possibly leaving you a free direct attack to your opponent.
Most "/Assault Mode" monsters can use this card for an OTK. For example, attack with "Stardust Dragon/Assault Mode", then activate "Assault Slash" to destroy "Stardust Dragon/Assault Mode" and Special Summon "Stardust Dragon" and attack again. Then use another "Assault Mode Activate" for an additional "Stardust Dragon/Assault Mode". This will inflict 3000+2500+3000=8500 damage. If your opponent has monsters on the field, simply use two copies of this card to achieve a similar result.
Activate "Ojama Trio" or "Nightmare Archfiends" to do even more damage to your opponent. The Tribute cost of "Nightmare Archfiends" will mean nothing as all monsters will be destroyed anyway. Just don't Tribute your "/Assault Mode" monster as it won't get its last effect.