"What's your plan? Some clever sciencey-spacey thing I won't understand?"

Dan Lewis

Noncreature, non-Equipment artifacts you control are Equipment in addition to their other types and have "Equipped creature gets +1/+0" and equip {1}.
Doctor's companion (You can have two commanders if the other is the Doctor.)

Doctor Who

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.

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 Equipment that's also a creature can't be equipped to anything unless it has the reconfigure ability.

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

If an artifact affected by Dan Lewis later becomes a creature, Dan's effect no longer applies to it. That artifact will stop being an Equipment and become unattached from any creature it was attached to; it will remain on the battlefield. The same thing happens if Dan leaves the battlefield.

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.

The affected artifacts retain their other types and abilities.

While Dan is on the battlefield, an Aura enchantment that somehow becomes an artifact in addition to its other types will also become an Equipment. Any of its abilities that refer to either "enchanted creature" or "equipped creature" refer to the creature it's currently attached to. It can be attached to other creatures using its equip ability. If you try to attach the Aura Equipment to a creature it can't legally be attached to, it remains where it is. If the creature it's attached to becomes an illegal permanent for it to enchant, the Aura Equipment will be put into its owner's graveyard as a state-based action.