Anatomy of "By Doing X, ... May Digivolve ... With the Cost Reduced by X"

Digivolution-granting text comes in two flavors:
- "... may digivolve into ..." (the card digivolves itself / lets another card digivolve)
- "Digivolve it into ..." (forces another card's digivolution)

BT25-092 Asuna Shiroki and BT6-060 Deputymon use the "may digivolve" construction, and both count as "digivolving effects" — digivolutions carried out by a card's effect.
They run on a different mechanism from normal digivolution (the main-phase action of stacking a card from your hand).

The "by doing X" in the text is an optional processing condition (15-7-1).
- Only if you choose to execute what it names (suspend this Tamer, trash from digivolution cards, trash from hand...) can the rest activate
- Decline it, and the "may digivolve with the cost reduced" part never happens

Details in the companion column "'By Doing X' and 'Also'."

With two BT25-092 Asuna Shiroki in the battle area, activating both [Main] effects at once for a combined -2 is impossible (Q6435).
- Basis: 15-8-4-1 (activation-type effects are optionally activated by the player) / 15-8-4-2 (declared when there is no unresolved processing)
- Activation-type effects are declared and resolved one at a time; digivolving effects are no exception

More in the companion column "Digivolution Cost Reduction: Can Multiple Copies Stack?"

BT25-082 BlackGatomon's [All Turns] effect: "while you have a Tamer with [Three Musketeers] in its text, this Digimon may digivolve into a Digimon card with the [Three Musketeers] trait, ignoring its digivolution requirements, with a digivolution cost of 4."
- "Ignoring the requirements" and "cost of 4" coexist in one effect
- It can digivolve into a used dual card via Arts Digivolve (Fly Bullet and friends) (Q6390)
- It can digivolve into Beelstarmon ACE during the opponent's counter timing (Q6391)
- It can activate together with digivolving effects like P-108 Wisdom Training (Q6392)

Details in the companion column on ignoring digivolution requirements.

Two "ignore the requirements" effects, one difference — a location phrase:
- BT6-060 Deputymon: "may digivolve into a Digimon card with the [Three Musketeers] trait **in your hand** ... cost of 6" → "in your hand" is specified, and a used Option card belongs to no area (9-1-4 / 9-1-5), so it can't be the target
- BT25-082 BlackGatomon: "may digivolve into a Digimon card with the [Three Musketeers] trait ... cost of 4" → no location phrase, so an Arts Digivolve target qualifies

The location wording decides it.

- 15-7-1 (optional processing conditions: "by doing ...")
- 15-8-4-1 to 2 (activation-type effects)
- 8-1 (digivolution in general)
- 8-1-2-2 (ignoring digivolution requirements)
- 9-1-4 / 9-1-5 (used Option cards belong to no area)

The checklist:
1. Choose whether to execute the "by doing X" (optional condition)
2. If you do, the "may digivolve with cost -X" activates as an activation-type effect
3. Multiple copies never activate at once — declare one at a time
4. A location phrase ("in your hand") restricts the target pool to that area
5. With "ignoring the requirements" attached, the requirements are never referenced