How does Octopus Umbra interact with effects that change the base power and toughness of, and counters on, a creature?

Question

Context

My friend plays a Commander deck, lead by Tuvasa the Sunlit:

Tuvasa the Sunlit gets +1/+1 for each enchantment you control.

She's in play and has +2/+2 — not counters — from the two enchantments on his battlefield. Then he plays Octopus Umbra, which reads:

Enchanted creature has base power and toughness 8/8 [...]

and continues in the rulings with:

Octopus Umbra overwrites all previous effects that set the creature’s base power and toughness to specific values. Any power- or toughness-setting effects that start to apply to a creature after Octopus Umbra becomes attached to it will overwrite this effect. (2018-07-13)

Any power- or toughness-modifying effects (those that give +N/+N, for example) and counters will apply to the creature’s new base power and toughness, even if they started to apply before Octopus Umbra became attached. (2018-07-13)

A judge explained to him that, when playing the umbra, every effect prior to playing the umbra disappears, and the new base power and toughness becomes 8/8. He explained that it has to do with the order of layers, which is still new and relatively confusing to myself and our table.

Now after reading the rulings, I'm confused about the "everything gets removed" part. How about Tuvasa's "passive" ability, which increases her P/T due to the amount of controlled enchantments? Isn't that checked constantly, making Tuvasa a 8/8 with +3/+3 from the enchantments?

Did we misunderstand the judge? Or is there something else we're missing? Any clarification would be much appreciated.

Question, in short

1. In this scenario, what is Tuvasa's power and toughness when playing the umbra? Please take in consideration the example where the umbra itself will be the third enchantment on his battlefield.
2. Do counters stay on the permanent when enchanting it with Octopus Umbra? Say Tuvasa also had a +1/+1 counter before the umbra came into play. My guess is that the counter stays, since they are placed on top of the base P/T, but I can't find the rules which support or contradict this.

Answer 1

The judge's ruling was correct. The various modifiers to power and toughness are applied in layers, and the 8/8 base P/T are in a different layer than the +1/+1 for each enchantment. With the three enchantments in your scenario (Octopus Umbra plus two others), Tuvasa the Sunlit will be 11/11 overall.

There are many continuous effects that can modify objects. They are applied in layers. Effects that modify power and/or toughness are applied in layer 7, and layer 7 has another 5 sub-layers. They are applied in the following order:

613.3a Layer 7a: Effects from characteristic-defining abilities that define power and/or toughness are applied. See rule 604.3.

Example: "This creature's power is equal to the number of knights you control".

613.3b Layer 7b: Effects that set power and/or toughness to a specific number or value are applied. Effects that refer to the base power and/or toughness of a creature apply in this layer.

7b is where the 8/8 modifier from Octopus Umbra is applied. It overwrites its original 1/1.

613.3c Layer 7c: Effects that modify power and/or toughness (but don’t set power and/or toughness to a specific number or value) are applied.

7c is where the +1/+1 per enchantment from Tuvasa the Sunlit is applied.

613.3d Layer 7d: Power and/or toughness changes from counters are applied. See rule 122, “Counters.”

613.3e Layer 7e: Effects that switch a creature’s power and toughness are applied. Such effects take the value of power and apply it to the creature’s toughness, and take the value of toughness and apply it to the creature’s power.

Answer 2

The explanation the judge gave you was unnecessarily confusing. Nothing disappears or gets removed. Some things get overwritten, but they're still there.

1. With three total enchantments out, one of them being Octopus Umbra enchanting her, Tuvasa the Sunlit will be 11/11. This is from her base power toughness being 8/8, and from her getting +3/+3 from her ability.
2. The +1/+1 counter would stay. In the same scenario, if she also had a +1/+1 counter on her, Tuvasa will be 12/12.

What's the layer system doing for us here?

Lots of us struggle with the layer system; it's fine that you are too. The layer system is defined rule 613, Interaction of Continuous Effects.

To know what Tuvasa is going to look like, first let's take a look at how the layers are going to apply the effects in this scenario. In particular we're working with layer 6 (ability-adding effects) and 7 (power/toughness effects).

Layer 6:

• Octopus Umbra gives Tuvasa a new ability (“Whenever this creature attacks, you may tap target creature with power 8 or less.”):

  613.1f Layer 6: Ability-adding effects, ability-removing effects, and effects that say an object can’t have an ability are applied.

Layer 7: This layer has a whole section covering how to apply it (rule 613.3) so we'll work through that too.

• Octopus Umbra sets Tuvasa's base power/toughness:

  613.3b Layer 7b: Effects that set power and/or toughness to a specific number or value are applied. Effects that refer to the base power and/or toughness of a creature apply in this layer.

• Tuvasa's own ability increases her power/toughness:

  613.3c Layer 7c: Effects that modify power and/or toughness (but don’t set power and/or toughness to a specific number or value) are applied.

• Tuvasa might also have a +1/+1 counter:

  613.3d Layer 7d: Power and/or toughness changes from counters are applied. See rule 122, “Counters.”

Now let's apply those layers.

1. Layer 6: Tuvasa the Sunlit gains her ability (“Whenever this creature attacks, you may tap target creature with power 8 or less.”). This doesn't affect the rest of our calculations.
2. Layer 7b: Tuvasa normally has base power/toughness 1/1. We'll now set it to 8/8.
3. Layer 7c: Tuvasa is currently an 8/8. Her ability gives her a further +3/+3. This would make her now an 11/11.
4. Layer 7d: Tuvasa might have a +1/+1 counter on her, which would further increase her to 12/12.

Thus our result: Tuvasa looks the same but has an additional ability and is 11/11 or 12/12.

I believe when the judge said "everything prior to the effect disappears", he was referencing the ability for the layer system to result in overrides. Tuvasa's power/toughness was overwritten. If Tuvasa was enchanted with both Kenrith's Transformation and Octopus Umbra, the layer system would tell you the most recent one "wins", overwriting the other to set Tuvasa's P/T to either 3/3 or 8/8. Both effects would still be there and neither would have disappeared, just one would be overwritten.