This would be a spell or unit unlocked at TH7, and could take the form of either a spell or ranged unit:

Name of Spell: Convert
Training Cost: Either in Elixir (starting at 25,000 and scaling by 5K each level) or DE (starting at 1,000 and scaling by 200 each level)
Targets: Enemy clan castle troops
Effect Type: radius of effect should be double that of lightning, but smaller than heal or rage
Damage Type/Amount: N/A
Training Time: 25 minutes (plus 5 min each level)
Description: Causes clan castle troops to convert to your side and join in your attack against the enemy base
Research/Spell Levels: Four, where each level allows conversion of higher leveled CC troops (i.e., 1st level, you can convert CC barbs/archers/goblins, 2nd level converts giants/balloons/wizards, 3rd level converts healers/minions/hogs, and 4th level converts anything)
Lab Level: 5

/OR

Name of Troop: Monk
Training Cost (in Elixir or DE): 10,000 elixir or 100 DE
Training Time: 18 minutes
Housing Space: 6
Damage per second: Does 8 DPS at lvl 1 if there are no enemy CC troops visible (essentially tracks w/ Barbs per level up to 4), has ranged ability (equal to archers) to convert enemy CC troops (same conversion abilities at each level identified above) - fires "convert" ability across entire target radius once every 2 seconds
Hit Points: starts at 65 (100 at lvl2, 135 at lvl3, and 185 at lvl4)
Movement Speed: 15
Description: converts visible enemy CC troops; if no visible enemy CC troops, does basic melee attack
Reference Art: http://ivilai.deviantart.com/art/Fra...Face-195021015