The poly supertype means Orb of Origin’s first ability doesn’t cost {T} to activate (unless another Orb of Origin is also on the battlefield).

Orb of Origin’s last ability applies only while it’s on the battlefield. It grants the mono and continuous supertypes to other noncreature artifacts on the battlefield.

Having multiple Orb of Origins on the battlefield will have no additional effect on artifacts on the battlefield except that the Orb of Origins will also make each other mono and continuous.

To activate an ability of a permanent with the mono supertype, if that ability’s activation cost doesn’t already include {T}, activating that ability costs an additional {T} to activate.

A permanent with the continuous supertype has no abilities as long as it’s tapped.

While Orb of Origin is on the battlefield, activating abilities of other artifacts may cause them to lose other relevant abilities when they become tapped. For example, if you activate Thought Vessel’s “{T}: Add {C}” ability, it’ll lose its “You have no maximum hand size” ability as long as it remains tapped. Similarly, activating Sword of the Meek’s equip ability (which costs an additional {T} while Orb of Origin is on the battlefield) will cause it to lose “Equipped creature gets +1/+2” as long as it remains tapped.

Playtest cards aren’t legal for play in any tournament format other than Mystery Booster Limited formats. On the other hand, we expect they will spice up a wide variety of non-tournament games (as long as everyone’s on the same page about using them!).

Playtest cards use a modified version of game symbols, such as {T} and {W}. These modified symbols should be treated as the standard symbols during play.

For many playtest cards, you’ll need to make a generous assumption that basic game rules would be updated to allow them to work. The Mystery Booster 2 Playtest Card Notes section (reproduced here in individual Gatherer rulings) provides guidance for fitting these cards into the existing rules structure.