(The key was to use the first question to dictate the answer of the second question
23 Lonis, Cryptozoologist Get A Clue For the low cost of two mana, Lonis, Cryptozoologist is a commander who allows you to convert your creatures into an impressive value engine, investigating (creating clue tokens) whenever another nontoken creature enters the battlefield under your control
Red Suns Twilight is another option, and one I like quite a bit more than By Force, considering the potential upside
This may vary from build to build, though youll need some help from blue to answer large creatures like Balamb T-Rexaur
Outside of those specific decks, Murder is always going to be the best choice for slaying others because its an instant and has no targeting restrictions
Ultimately, Dinosaurs are an incredibly fun creature type to explore, so lets swoop down, much like a Pteranodon, and explore the best Dinosaur cards for Commander