ライアン・シンクレア

ライアン・シンクレアが攻撃するたび、土地でないカード１枚が追放されるまで、あなたのライブラリーの一番上から１枚ずつ追放していく。その追放されたカードの呪文としてのマナ総量がライアン・シンクレアのパワー以下であるなら、それをマナ・コストを支払うことなく唱えてもよい。これにより追放されて唱えられなかったすべてのカードをあなたのライブラリーの一番下に無作為の順番で置く。
ドクターのコンパニオン

Ryan Sinclair

Whenever Ryan attacks, exile cards from the top of your library until you exile a nonland card. You may cast the exiled card without paying its mana cost if it's a spell with mana value less than or equal to Ryan's power. Put the exiled cards not cast this way on the bottom of your library in a random order.
Doctor's companion (You can have two commanders if the other is the Doctor.)

Doctor Who

Although Doctor's companion is a new variant of the partner ability, the rules for partner have not otherwise changed. Notably, Time Lord Doctors and cards with Doctor's companion do not interact with cards which have another partner ability.

An effect that checks whether you control your commander is satisfied if you control one or both of your two commanders.

Both commanders start in the command zone, and the remaining 98 cards (or 58 cards in a Commander Draft game) of your deck are shuffled to become your library.

If something refers to your commander while you have two commanders, it refers to one of them of your choice. If you are instructed to perform an action on your commander (e.g. put it from the command zone into your hand due to Command Beacon), you choose one of your commanders at the time the effect happens.

If your Commander deck has two commanders, you can include only cards whose own color identities are also found in your commanders' combined color identities.

Once the game begins, your two commanders are tracked separately. If you cast one, you won't have to pay an additional {2} the first time you cast the other. A player loses the game after having been dealt 21 combat damage from any one of them, not from both of them combined.

The Doctor's companion ability allows you to have two commanders if one has the ability and the other is a legendary creature that is a Time Lord Doctor and has no other creature types. Creatures with the changeling ability, for example, can't be a second commander this way.

You cast the spell as part of the resolution of Ryan's triggered ability. You can't wait and cast the spell at a later time.

You may pay optional additional costs to cast that spell, such as kicker costs. If it has any mandatory additional costs, you must pay those.