Can you pendulum summon twice?
Consequently, do you have to tribute to pendulum summon?
Answer: No. Placing a pendulum scale takes a spell/trap zone, not a monster zone, and playing your card this way treats it as a continuous spell, not a monster. Therefore, it doesn't have the qualities of a monster and can't attack, defend, or be tributed for a tribute summon.
Also to know, what cards can you pendulum summon?
A Pendulum Summon is a type of built-in Special Summon, so it can be negated by cards like "Solemn Warning" and "Thunder King Rai-Oh"; however, if more than 1 monster would be Pendulum Summoned at the same time, cards like "Black Horn of Heaven" (which specify they can only be activated when exactly 1 monster would be
Pendulum monsters by themselves aren't too broken. While people like to complain about their ability to recycle, they don't do anything that contribute to themselves being broken that other decks cannot do.