#copying abilities

When you cycle Yidaro, you put its cycling ability on the stack and then its triggered ability triggers and resolves before you draw a card.

Mairsil won’t transform but you’ll still get Treasure tokens.

When Mairsil’s copy of the Treasure Map ability resolves, the ability will do as much as it can. This means that you’ll scry 1 and put a landmark counter on Mairsil, then because there are three landmark counters on Mairsil, you’ll remove all landmark counters from him. You can’t transform Mairsil because he’s not a double-faced card, so that instruction can’t happen and is skipped, but you’ll still continue resolving the effect and create three Treasure tokens.

You’ll search your library for Squadron Hawks.

While normally a card that gains an ability from another card will substitute its name for the name of that card in the gained abilities, this only applies when the ability is referring to that card itself. It doesn’t overwrite its own name onto abilities that specify a card name, so when Sakashima, as a copy of Squadron Hawk, has its trigger tell you to search for “cards named Squadron Hawk”, that instruction isn’t changed.

Mairsil can use those abilities just fine. When a card refers to itself by name, it just means itself and not any other card with the same name. In the case of Mairsil or other effects that copy abilities to other cards, they work the same with Mairsil's name substituted for Arcanis's in the appropriate places. (Quicksilver Elemental actually has reminder text about this. Useful reminder text. Wow!)Note that this isn't the case for cards that actually look for cards with specific names, such as Squadron Hawk or cards with Grandeur abilities.

You choose the target for the copy of the ability. There's no randomness involved here.

The copy of the ability is created with the same target as the original ability and will keep that target if you choose not to change it.

When the first (copied) ability of Memory Jar resolves, each player will exile all the cards in their hand (Hand A) and then draw seven cards. It also sets up a delayed trigger for the end step. Players can activate abilities and cast instants and spells with flash before the other Memory Jar ability resolves, as normal. 

When the second (original) ability of Memory Jar resolves, each player will exile all the cards in their hand (Hand B) and then draw seven cards. It also sets up a delayed trigger for the end step. Players can cast spells and activate abilities as normal until the end step.

When the end step begins, both of the delayed triggers go on the stack and you get to choose their relative order. This means you choose whether or not players will get back Hand A or Hand B first. Whichever choice you make, players will discard their current hands then return the Hand A or Hand B to their hands.  Players can activate abilities and cast instants and spells with flash before the other delayed trigger resolves, as normal. When the second delayed trigger resolves, players will discard what’s left of the first returned hand and then get back whichever of A or B wasn’t returned to their hands by the first trigger.