If you want a Pokemon that is good at taking hits, but doesn't so anything back, then Umbreon is good. Otherwise, mandibuzz and Tyranitar work well too. I'd mention sableye, but...he's not really a wall in any sense. I haven't tried spiritomb this generation.
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Wall - Need reliable recovery - or a niche to function perfectly well whilst asleep (e.g. resttalk/chestorest). Requires good HP and Defenses. Needs access to status inducing damage. Burn or Poison. Optional some form of defensive buff or team support. Attacking move revolving around - Amount of damage recieved. Opponents attack stat. Or current HP.
Tanks however can have buffed up defenses (normally one of the other) whilst functioning in a primarily attacking role with additional switch in capabilities. Tyranitar for example can make a decent special tank under sandstorm. Scrafty is a useful status tank with shedskin and dragon dance/drain punch.
Drapion can function as Phaser support with spikes and whirlwind. Or crit happy (with Sniper + scope lens + Night slash, corss poison etc)
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