Looking at a Tempest Cleric grappler. There are a few things you can do here, but it's all going to be pretty feat-intensive...
The class itself has some fun things to offer the overall grappler archetype. There's heavy armor proficiency from the get-go, a reactive shock ability that uses a DEX save (meaning that if you've taken the Grappler feat you can restrain someone and force them to make such saves at a disadvantage), Destructive Wrath is a pretty decent usage of CD in general (and pretty hilarious with Call Lightning), and you can apply 1d8 (later 2d8) thunder damage to any weapon attack, which
technically includes kicking one of the two grappled opponents you're keeping your hands full with. Additionally you get the option when dealing lightning damage to shove the target 10' away from you, which can be useful when you've dragged someone to within 10' of a precipice or just want enemy number 3 to piss off.
Clerics also get the lovely Enhance Ability spell to make strength checks at an advantage, Spiritual Weapon to smack whoever you've cornered, and more tasty bits.
The problem of course is that you'd like to have War Caster as a minimum, and both Grappler and Shield Master would be great to have on top of that. There's also no clean way of getting Expertise, but I suppose if you wanted to focus on single-target stuff you could dip into rogue and pick up sneak attack so you could grab 'n' stab someone with a thunderous rapier after grappling and shoving them to get advantage. It'd be lovely to have something like Create Bonfire (if/when you're not using Enhance Ability) to use with Grappler, since you could just pin someone in the fire to make them keep taking disadvantaged DEX saves while being toasted like a Manmallow (and you can keep attacking them with other things so long as you maintain concentration!)... But that would involve dipping into probably Druid, since the Magic Initiate feat is
yet another feat.