What stats does Radiant Crownguard give?

Radiant Crownguard grants 40 AP and 200 HP.

What kind of item is Radiant Crownguard in TFT Set 17?

Radiant Crownguard is a Radiant item in TFT Set 17.

Yes — Radiant Crownguard enables a Shield effect.

Combat Start: Gain a 50% max Health Shield for 8 seconds.

radiant

Combat Start: Gain a 50% max Health Shield for 8 seconds.

When the Shield expires, gain 50% Ability Power.

Shield

Grants temporary HP that absorbs damage before the unit's real Health is touched.
Ability Power

Scales with Ability Power (AP). Champions and effects flagged as AP-scaling get bigger damage, healing, or shield values when the holder stacks AP from items like Jeweled Gauntlet, Rabadon's Deathcap, and Nashor's Tooth, or from trait bonuses.

Max Health

Grants the unit additional maximum HP, either flat (like +150 Health) or percentage (like +6% max Health). It comes up whenever you stack Giant's Belt items, pick health-boost augments such as Yasuo's Golden Hex or Giant and Mighty, or play Cho'Gath, whose cast permanently raises his own max Health every time he eats an enemy. For the cross-round permanent stat-stacks angle specifically, see the dedicated permanent stat-stacks page.