Woops wrong set

Also, it appears to have about 3 cards worth of text.

And... yowsers. What abilities they are! "Activate target planeswalker's ultimate for +1". Or heck, a bunch of other overpowered stuff too. At least it can't power its own ultimate...

You’d still have to have enough loyalty to activate the ultimate in the first place, but yeaaaaah

Actually I’m not sure how replacement effects work with costs. Perhaps you wouldn’t be able to activate a minus ability of it at all

From Solemnity Rulings:

If the cost of an ability or an additional cost of a spell requires putting counters on an artifact, creature, enchantment, or land, that cost can’t be paid...

The comprehensive rules treat “can’t” effects similarly to replacement effects, so I imagine you simply can’t use minus abilities on planeswalkers targeted by that.

> The comprehensive rules treat “can’t” effects similarly to replacement effects, so I imagine you simply can’t use minus abilities on planeswalkers targeted by that.

I don't know where you get this, but your reasoning leads you to the wrong conclusion. Replacement effects and "can't" effects are entirely different. You may be confused because resolving effects that are partially prohibited causes you to skip part of the effect and there are certain replacement effects that replace events with "do nothing instead".

To pay a cost you perform the original action with all replacements applied, but consider the post as if no replacement was applied e. g. if a cost involves milling yourself ("put ... into your graveyard") and a static ability causes the cards to go to another zone (e. g. exile) the cost is paid even if no card is put into the graveyard this way.

Another example from a quickly googled FAQ:

> Q: If there’s a Sulfuric Vortex in play, can you cast an Invigorate for its alternate cost?

A: Yes. Sulfuric Vortex replaces any life gain with no life gain, but it doesn’t prevent players from trying to gain life. Even though when you pay the cost, it will be replaced by something much less useful, the game will still see that and count the cost as being paid.

That means this card indeed allows you to chose a cost requiring to remove counters and add one of those counters instead.

As you state that's not entirely problematic on ultimates since you still need to accumulate counters, but it gets out of control on X-costs e. g. Huatli, Warrior Poet and Sorin, Grim Nemesis.

That's why some effects like Doubling Season used the wording "If an effect would put one or more counters on a permanent you control, it puts twice that many of those counters on that permanent instead." specifying an effect. Many replacement effects use "effect" or "spell or ability an opponent controls" etc. if they are replacing an even that commonly is a cost (e. g. discard on Loxodon Smiter) to cut out degenerate interactions of this sort.

Ah. I see. Well I can fix that, then.