Hello there,
As per Wiki:
According to the above I added exactly 5 forma to this weapon, so we can obtain Mastery Points from it.
In this case I suggest you to pick Radiation/Heat element.
As for Exilus I picked Cautious Shot, Tonkor has self-stagger, that happened after some changes (self-stagger instead of self-damage) so to prevent this I had to change Exilus mod for something that can help you with that.
Alternatively, you can wear Primed Sure Footed on any of your Warframe - excluding Atlas (Prime) - gaining 100% chance that a Warframe will resist knockdowns and staggers.
Bane of Faction mod is flexible, change it according to the faction you are up against, or simply put [Serration].
Enjoy, THeMooN85