Tam, the Possibility: Type Matters, Not the Walker

With Tam, the Possibility, the planeswalker of a type you don't yet have on the battlefield wins out, not the most powerful one.

The Hidden Rule: Types Count, Not Walkers

Tam's ability makes you proliferate X times, where X is the number of different planeswalker types among those you control. Not the number of walkers.

Consequences:

• A second Garruk Wildspeaker when you already have a Garruk on the battlefield doesn't add a proliferate.
• Jiang Yanggu, Wildcrafter does: it's a new type, so X goes up by one.
• The selection criterion changes: what counts is the variety of subtypes, not the power of the individual walkers.
• Seven-mana bombs like Vraska, Regal Gorgon pay an enormous cost for a single increase to X, the same one you get from a three-mana walker.

Tam already costs five colors to activate, so every mana saved on walkers is tempo gained.

The Small Walkers That Pay Off the Discount

Tam reduces the cost of planeswalkers by . Cheap walkers of a new type thus become nearly free, and each one raises X.

• Jiang Yanggu, Wildcrafter: three mana, two with the discount. The −1 puts a +1/+1 counter on a creature, making it a mana source of any color. In a five-color deck it serves as fixing and ramp at once.
• Jace, Cunning Castaway: three mana, two with the discount. The −2 makes a 2/2 Illusion, and the −5 makes two nonlegendary copies of itself, which are still the same type and don't raise X. The value lies in the extra loyalty to proliferate and the types it brings onto the battlefield.
• Kasmina, Enigmatic Mentor: four mana, three with the discount. It creates a 2/2 Wizard, filters your hand, and makes your opponents' spells that target your creatures or your walkers more expensive.

They're underrated because nobody looks at them: they seem weak in absolute terms. With Tam they do exactly what's needed, which is to enter the battlefield early and bring a new type along.

Keeping Them Alive: Cleanup and Protection

A walker deck loses if the walkers die before they've been proliferated.

• Kasmina, Enigmatic Mentor taxes your opponents on spells that target your creatures or your walkers. It's the cheapest passive protection on the list.
• The Elderspell destroys any number of target planeswalkers, and you get two loyalty counters for each one on a walker of yours. Against a hand full of opposing walkers it's a spike of value. It does cut both ways, though: you can target your own too, but that makes no sense with Tam. Use it only against other players' walkers.
• Eaten Alive costs if you sacrifice a creature, otherwise . It exiles a creature or a planeswalker.
• Worthy Cost costs and requires a sacrifice. Same exile effect on a creature or planeswalker.

The two removal spells cost one mana at most and fit well with the tokens your walkers produce. They leave the table clear of threats and of opposing walkers competing for the same types.

The Traps That Look Like Synergies

The semantic filter pushes up cards that sabotage the plan. The ones to avoid:

• The Immortal Sun: it stops you from activating planeswalkers' loyalty abilities, so you no longer accumulate counters to proliferate. It draws cards and reduces costs, but it shuts down the core of the deck.
• Single Combat: each player chooses a creature or a planeswalker and sacrifices the rest. You lose almost all of your walkers, the opposite of what you want.
• Plaguecrafter: each player sacrifices a creature or a planeswalker. If you have Tam and other walkers, sacrificing something is a real cost, and it only works if you have a spare creature within reach.

These are cards that "talk" about planeswalkers in their text, but they work against the strategy.

The List in Brief

Play right away:

• Jiang Yanggu, Wildcrafter, Jace, Cunning Castaway, and Kasmina, Enigmatic Mentor: walkers of different types, cheap, discounted by Tam.
• Eaten Alive and Worthy Cost: one-mana removal that also hits opposing walkers.
• The Elderspell: only if the table is full of opposing walkers to sweep away.

Leave in the binder: The Immortal Sun, Single Combat, Plaguecrafter.

Verdict: in five colors the fixing is free, so the bottleneck is the variety of types. Every slot given to a walker of a type you already have is a wasted slot.