Short Answer

Increase your Fighting and Vigor, get Arcane Background (Chi Mastery) and deflection, use a spear (Str+d6, Parry +1, Reach 1) for a weapon, and use good tactics. Also, double-check that you are using the correct rules for ranged weapons at melee range.

Long Answer

Let's review what a tank is

According to Wikipedia:

tanks redirect enemy attacks or attention toward themselves in order to protect other characters or units. Since this role often requires them to suffer large amounts of damage, they rely on large amounts of vitality or armor, healing by other party members, evasiveness and misdirection, or self regeneration.

So the parts that make up a tank are:

• Redirect attacks towards yourself
• Survive multiple attacks via one or more of the following:
  • Armor
  • Receiving healing
  • Evasiveness
  • Self-regeneration

You've added an additional criteria: "able to Shake", which we will assume means able to do enough damage to affect a fight, but not expected to do a significant amount

Redirect attacks towards yourself

There is no way in core Savage Worlds or Deadlands Reloaded to force an opponent to attack you instead of an ally, and that's by design.

The best way to fill this role is to be the most immediate threat. You've got the right idea that you should be a melee fighter in this case, especially in a gun-heavy setting like Deadlands for a number of reasons:

• Characters who emphasize gunfighting tend to have a low Fighting (and thus a low Parry), and usually rely on cover, which is irrelevant in melee combat
• Guns larger than a pistol cannot be fired in melee
• Shooting rolls for pistols and smaller guns must be greater than or equal to your Parry, rather than the standard target number of 4
• Ranged enemies have a chance of hitting their ally via the Innocent Bystander rules.

I'm a little surprised that you said you were having trouble if enemies had guns, so I think you should double-check to make sure you are following those rules correctly.

The main downside to attacking in melee is that enemies can get a Ganging Up bonus against you. However, the Deadlands Reloaded Martial Arts Edge makes you immune to that, so you're right to take that. _{This is a really broken effect that has not appeared in any future settings, and I am absolutely certain it will be removed in a future version of Deadlands Reloaded.}

Recommendations:

• Rely on melee combat
• Take the Martial Arts Edge
• Make sure that your table is following the rules for ranged weapons in close combat

Survive multiple attacks via one or more of the following

Armor (i.e. Toughness)

Armor as such doesn't really exist in the Deadlands setting because all pistols have Armor Piercing 1, and all rifles have Armor Piercing 2. Sure, you could have the equivalent of plate mail by strapping cast iron to your chest, as in Back to the Future Part III, but for all intent and purposes, there is no armor in Deadlands.

However, Savage Worlds does have Toughness, which makes you shrug off or otherwise not be affected by damage. You'll want a high Vigor for that, both for soak rolls and a high Toughness.

There are a couple of other ways to improve Soak rolls and increase Toughness:

• Obese Hindrance (+1 Toughness, but –1 Pace and d4 Running Die)
  • This hurts a melee character since they have a more difficult time closing the distance. If you're fighting in close quarters frequently, this may be worth taking
  • That said, Hindrances are supposed to be hindering. If you were my player, I would probably put you in more situations where you have to run to close melee more often.
• Elan (+2 when spending a Benny on a Trait roll (including Soak rolls))
• Luck / Great Luck (+1/+2 Bennies)

There is also Brawny, which grants +1 Toughness, but it's almost always better to just increase your Vigor if you are able to, since you get +1 Toughness anyway as well as better Soak rolls.

Let's not forget getting out of Shaken as well. Assuming you are using the revised Shaken rules from May 2015, you shouldn't have too much trouble getting out of Shaken with a decent Spirit. If you are having trouble, the Combat Reflexes Edge helps a lot.

You mentioned "a Shaman with bear stance" as a possible character option, presumably for the increased Toughness. I'm going to guess you mean the shape change power, but changing into a bear is only available to Heroic characters, so that is not available to a Novice character.

Receiving healing

There isn't really anything that an individual character can do to help with this. Having someone in your party who can cast magical healing can help a great deal (non-magical healing via the Healing skill takes 10 minutes, so is too slow for combat).

Evasiveness

There are two types of evasiveness: melee and ranged. Melee evasiveness is tied to Parry, which is increased by Fighting. Fortunately, Fighting is a skill that you'll already have a lot of as a melee fighter. Boost that as high as you can. This will also help against ranged combat in close quarters, since enemies shooting pistols at you point blank have to go against your Parry, instead of the usual target number of 4.

If you frequently fight in open areas, consider the Dodge Edge, which gives –1 penalty against ranged attacks. If you fight in closed quarters or areas with lots of cover, skip this and use better tactics by taking cover, crouching, taking advantage of dim light, etc. (See How do I improve my ranged defense in Savage Worlds for more information on how to improve ranged defense, especially through tactics).

The best way to get better at evasiveness is through the deflection power, which provides a –2 penalty to both melee and ranged attackers trying to hit you (–4 with a raise). I'm baffled that you said this was something you tried that didn't work for you, as this is an incredible way to avoid taking damage. At my table, I frequently have trouble hitting players who have this up.

Also, don't forget that martial artists get an extra benefit with deflection:

The martial artist may make an immediate Agility roll at –6 for bullets or –4 for thrown weapons.

If successful, he hurls the projectile back at the original target for Str+d6 damage. Called seize the pearl of death.

Self-regeneration

Casting the healing power on yourself would cover this, but to be honest, it's better if you can get someone else to do this for you.

There is the Knack (Breech Birth) Edge in Deadlands Reloaded, which allows you to spend a Benny to automatically heal one wound without a roll. If you find yourself soaking one wound, this may be an option for you.

Recommendations:

• Boost your Vigor
• Increase your Fighting, which increases your Parry
• Get the deflection power (probably through Arcane Background (Chi Mastery) Edge)
• Consider the Dodge Edge if you are frequently fighting in open spaces, skip it if in close quarters
• Consider the Obese Hindrance if you are frequently fighting in close quarters, skip it if fighting in open spaces where you need to cover ground
• Use better tactics to avoid being hit by ranged attacks
• See if you can get another player to get the healing power and ask them to cast it on you when you need it.
• Consider the Combat Reflexes Edge to get out of Shaken more easily
• Consider taking the Elan Edge to give +2 to Soak rolls, or gain extra bennies with Luck/Great Luck.

Deal enough damage in a fight

We've already talked about increasing your Fighting, which helps your Parry (thus increasing your melee defense). Consider using tactics like Wild Attack and Gang Up bonus to improve your chance to hit.

I'd recommend not going bare-fisted with a martial artist. Instead, use a Spear (Str+d6, Parry +1, Reach 1, requires 2 hands)* This has two advantages: you become a threat to your enemies from one square away, and you increase your Parry even further, increasing your melee defense. I think of the two, the Parry +1 is more valuable than the Reach 1 because ranged enemies can shoot you at a TN 4 from one square away, but against your Parry adjacent. However, Reach is good against melee enemies, since they tend not to have it.

Honestly, I don't think that Edges like Superior Kung-fu: Wing Chun are worth it for your goal of being a tank, although it may be useful if you decide you want to attack more in the future.

* There are also more niche weapons, like the Sai (Str+d4, +1 Parry, +1 to Disarm), in Deadlands Reloaded: The Flood Player's Guide.

Miscellaneous

Arcane Background (Chi Mastery) gives you two powers. I've already strongly recommended deflection. As a second power, I recommend boost/lower trait, since that is a pretty versatile power. You can increase your Fighting or Vigor, or decrease your opponent's Fighting, Vigor, or Shooting.

Trash is anything with 5-6 parry and 5-6 Toughness.

Your GM is giving you a really tough time if Parry and Toughness 6 is "trash" for Novice characters. A Veteran Gunman has Parry 5 and Toughness 6, and they're supposed to be tougher. Is there any chance that you're expected to run?

As for the "boss", the Taxidermist has no obvious weaknesses. I recommend following the combat tactics on Pinnacle's Combat Survival Guide. He's got a high Parry, so your ranged allies staying out of melee and firing their guns is the easiest way to hit him. If they do a called shot, they should be able to do decent damage. In this particular case, the Taxidermist is stronger than you as a melee fighter, so I think your job is to just keep him busy and not worry about damaging him, just setting things up so that your ranged allies can shoot him. When fighting gunslingers, it will be your time to deal lots of damage.

Putting it all together

Putting this all together, I think that a Novice Deadlands Reloaded character would be optimized as a tank with the following build:

Attributes: Agility d4, Smarts d4, Spirit d8, Strength d6, Vigor d10

Skills: Boost/Lower Trait d8, Deflection d8, Fighting d10, +2 skill points

Charisma: 0; Pace: 6; Parry: 7 (+1 with spear); Toughness: 7

Hindrances: 1 major, 2 minor

Edges: Martial Artist, Arcane Background (Chi Mastery)

Powers: boost/lower trait, deflection

Gear: Spear (Str+d6, +1 Parry, Reach 1, requires 2 hands), $247

In melee combat and adjacent ranged combat, the enemy must roll an 8 or higher on their attack roll in order deal any damage. If deflection is up, they have to roll a 10 or a 12, depending on if they succeeded with a Raise. And in ranged combat, enemies need to roll a 6 or an 8 in order to hit if deflection is up. Even if they do manage to hit, they have to roll at least 7 damage to Shake, and there is a good chance they will soak any damage.

In addition, the character rolls Fighting d10 to attack with his spear, possibly from one square away, and will deal 2d6 damage. They also have the boost/lower trait power

The main flaw with this build is that they are extremely susceptible to Agility and Smarts Tricks, since they have a d4. A clever GM will exploit those. It may be good to put a d6 in those instead of pushing Toughness. Also, there are no social skills or other useful things, which may mean your character will be crippled in social situations or other non-combat encounters. A lot of skill points were spent by pushing Fighting above Agility, so a higher Agility means more skill points for other purposes.

The rest comes down to using tactics. And making sure you are following the correct rules for ranged weapons in melee combat.