If you wish to raise a creatures power so its mentor ability can target a bigger creature, the last chance you have to do so is during the beginning of combat step
Transformers introduces the mechanics More Than Meets the Eye , which allows a double-faced card to be cast with its back face up, and Living Metal , an alternative to the "Crew" mechanic that allows vehicles to become artifact creatures on their user's turn
Competitively, its really not the best pick, but thats a secondary concern for many
If you sacrifice a Human creature to Falkenrath Aristocrat, you can start tacking on +1/+1 counters to it
Vedalken Orrery Vedalken Orrery provides an effect that literally any decks happy to have, but its just hard to run a 4-mana do-nothing and hope you untap with it unscathed
Here are the general rules of thumb I follow when addressing this question myself: If my deck has green, the best mono green mana ramp spells are usually better than my multicolor options