And a couple of "responses" is good, ie "destroy target creature" or "exile target enchantment" Probably don't need more than 4-6 in a 60 card deck
But at this point in the OCG, Zoodiac is the only deck with a 1-card starter, whereas other decks like Metalfoes or ABC requires 2 3 cards to start, which means Zoodiac effectively only needs 3 or 4 disruptions to shutdown their opponents play
Etched Monstrosity is a 5/5 that you can pay to draw three cards while also turning it into a 10/10
Legality depends on the tournament format -- Toxic Scorpion can be legal in some formats and banned or restricted in others
As far as protecting one thing even yourself, if you for instance get targeted by Sorin Markovs downtick setting you to 10 life Deflecting Swat is probably the best option
C Common Absolute Crusader X EARTH Level 4 [ WarriorEffect ] ATK 1800 DEF 1200 If a Level 5 or higher monster(s) is Special Summoned: Tribute this face-up card