Sure, you'll have to do just once per turn, but it's instants so you can do it on opposing turns too
If you wish to raise a creature's 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
Now, his experience yielded fruit
With any 7th Edition foil under the sun popping off lately, we could be at a tipping point and if our money is finite, we may be able to identify cards from the ones that arent expensive already which ones have the most upside given EDH inclusion

Commander Decklist Creature 37 Cards 1 Morophon, the Boundless 1 Taurean Mauler 1 Avenger of Zendikar 1 Tendershoot Dryad 1 Harper Recruiter 1 Mirror Entity 1 Tazri, Beacon of Unity 1 Atla Palani, Nest Tender 1 Magda, Brazen Outlaw 1 Chameleon Colossus 1 Feline Sovereign 1 Realmwalker 1 Brenard, Ginger Sculptor 1 Bruse Tarl, Roving Rancher 1 Cloudshredder Sliver 1 Kirri, Talented Sprout 1 Rin and Seri, Inseparable 1 Rukarumel, Biologist 1 Sophia, Dogged Detective 1 Unsettled Mariner 1 Impostor of the Sixth Pride 1 Kinsbaile Cavalier 1 Amoeboid Changeling 1 Mothdust Changeling 1 Shapesharer 1 Graveshifter 1 Skeletal Changeling 1 Fire-Belly Changeling 1 Gemhide Sliver 1 Guardian Gladewalker 1 Harabaz Druid 1 Manaweft Sliver 1 Masked Vandal 1 Moritte of the Frost 1 Risen Reef 1 Bloodline Pretender 1 Universal Automaton Sorcery 7 Cards 1 Raise the Palisade 1 Stick Together 1 Kindred Dominance 1 Distant Melody 1 Cultivate 1 Farseek 1 Kodamas Reach Enchantment 6 Cards 1 Bitterblossom 1 Arcane Adaptation 1 Double Down 1 Kindred Discovery 1 Black Market Connections 1 The Bears of Littjara Kindred 4 Cards 1 Bitterblossom 1 Crib Swap 1 Shields of Velis Vel 1Nameless Inversion Instant 8 Cards 1 Kindred Summons 1 Crib Swap 1 Shields of Velis Vel 1 Arcane Denial 1 Pongify 1 Nameless Inversion 1 Beast Within 1 Spoils of Adventure Artifact 5 Cards 1 Coat of Arms 1 Maskwood Nexus 1 Sol Ring 1 Realmbreaker, the Invasion Tree 1 Arcane Signet Land 37 Cards 1 Adarkar Wastes 1 Brushland 1 Darkwater Catacombs 1 Exotic Orchard 1 Fabled Passage 1 Karplusan Forest 1 Llanowar Wastes 1 Mossfire Valley 1 Murmuring Bosk 1 Mutavault 1 Overflowing Basin 1 Secluded Glen 1 Sungrass Prairie 1 The World Tree 1 Yavimaya Coast 1 Ancient Amphitheater 1 Arcane Sanctum 1 Command Tower 1 Frontier Bivouac 1 Gilt-Leaf Palace 1 Jungle Shrine 1 Opulent Palace 1 Path of Ancestry 1 Seaside Citadel 1 Wanderwine Hub 3 Plains 3 Island 1 Swamp 2 Mountain 3 Forest Everyones Invited
