(1) "He can't be targeted by the effects of monsters Special Summoned from other than GY" is sometimes useful
Gyrus, Waker of Corpses XBRG Legendary Creature Hydra 0/0 Gyrus, Waker of Corpses enters the battlefield with a number of +1/+1 counters on it equal to the amount of mana spent to cast it
We also enjoy the cards that (gently) take the mick out of other TCGs too
Some Casters use cryptids to make trouble
A common case being on combat tricks like Ranger's Guile and Snakeskin Veil, and sometimes those big creatures that are hard to interact with are positive additions to their environments (looking at you, Carnage Tyrant)
Blue can also play combo-control, which means instead of stalling for time until a single giant creature is drawn, you can defend yourself until it is possible to cast a hidden combo for an instant win