Crystal shield is the most OVERPOWERED shield for multifights in the wild, the only requirements are roving elves quests and 70 defence and 50 agility.
Comparison vs a rune kiteshield: (34 more range defense bonus)
The first shield you're going to buy is going to cost 750k, after that its 600k > 450k > 300k and after that its 150k forever. Very cheap and OVERPOWERED.
Getting them:
Ilfeen will recharge crystal weapon seeds into crystal bows, crystal halberds, or crystal shields. She can be found teleporting back and forth between two clearings in Isafdar. After completing Song of the Elves, she can be found in the south-west part of Prifddinas.
Priff location:
Wiki: https://oldschool.runescape.wiki/w/Crystal_shield