On his standard card, Gandalf the Grey appears holding Glamdring, and offers the player multiple single-use abilities whenever they cast an instant or sorcery spell, including tapping or untapping a permanent, dealing three damage to each opponent, copying an instant or sorcery spell, or placing Gandalf on top of their library
Sure, the creature sacrifices itself at the end of the turn, but attacking and forcing your opponent to sacrifice most of their board is usually enough to put you ahead and win the game
The ability to cast any legendary spell, not just creatures, for three mana while you have a tapped creature to spare is a big deal
Jaw Lock might not deal much damage, but it stops your opponent from retreating, giving you the upper hand
Inspiring Call One of the best incentives to play around with +1/+1 counters, Inspiring Call can draw you lots of cards as well as protect your creatures from a wrath or combat situations