This strategy does not work well with the beast master. If you want a buddy build that plays defensively until it has enough power to take down the enemy, might I suggest using a malakai priest with guardian angel as your holy avenger? Then use armor, a couple temples of the dawnbreaker, a hand of bim shalla and a temple of light with a few cheap light attacks and some enchantments to power up yours and your angels attacks.
If you'd rather do a buddy turtle than a buddy tank, your best bet is anvil throne warlord with battle forge, grimson sniper and walls of pikes. When they try to get close, shoot with your sniper. Once you're warlord is powered up enough send him out to fight the enemy mage.
Your going to need some anti swarm tech for that to work though, as well as some ways to deal with a few big creatures. Sleep, tanglevine, quicksand, mangler caltrops, suppression orb, sandstorm, hail of stones, altar of peace, armor, defenses, etc.