Not to mention a built-in sacrifice effect can be very useful
Companion is the kind of mechanical innovation with a very obvious and in some ways reasonable motivation why not try to replicate the nuanced deck-building and reliable gameplay of Commander in other formats
Against a dark, cloudy background, Sephiroth steps to the right and looks ready to swing his wickedly long sword, Masamune
For example, you can use all Grizzly Bears shown above in your Modern format deck
We see three great spikes, Ramp at 24, Finishers/ Surprise /Alternate win conditions at 16 and Target Removal at 13 which are a result of our strategies: We need extreme Ramp to be able to play our big Dinosaurs that many act as Finishers and both them and our Enrage strategy lead us to have strong Target Removal
If the creature you don't control is an illegal target as Signature Slam tries to resolve but the creature you control is a legal target, you'll still put a +1/+1 counter on the target creature you control