We prove a character formula for some closed fine Deligne-Lusztig varieties. We apply it to compute fixed points for fine Deligne-Lusztig varieties arising from the basic loci of Shimura varieties of Coxeter type. As an application, we prove an arithmetic intersection formula for certain diagonal cycles on unitary and GSpin Rapoport-Zink spaces arising from the arithmetic Gan-Gross-Prasad conjectures. In particular, we prove the arithmetic fundamental lemma in the minuscule case, without assumptions on the residual characteristic.Here the product is over pairs {Q, Q * } of monic irreducible non-self-reciprocal polynomials in F q 2 [λ] with non-zero constant terms. Theorem 1.2.1 then follows immediately from Theorem 1.2.3 and the explicit formula for the analytic side given in [RTZ13, Proposition 8.2]. Remark 1.2.4. Theorem 1.2.3 is also used to prove the minuscule case of Liu's arithmetic fundamental lemma for Fourier-Jacobi cycles, see [Liu18, Appendix E].Remark 1.2.5. In Theorem 5.2.4 we also establish an analogous arithmetic intersection formula for GSpin Rapoport-Zink spaces arising from the AGGP conjectures for orthogonal groups. This provides a new proof of the main result of [LZ18], and also removes the assumption that p n+1 2 in loc. cit. 1.3. Computing the arithmetic intersection. The starting point of the proof of Theorem 1.2.3 is the observation made in [LZ17, Proposition 4.1.2] that, in the minuscule case, the formal scheme (1.1.2) can be identified with the fixed point scheme Vḡ of an explicitly given smooth projective variety V over k, under a finite-order automorphismḡ. It also turns out that Vḡ is an Artinian scheme. Hence Int(g) is given by the k-length of Vḡ.In order to compute the k-length of Vḡ, there are two apparent approaches. One approach, taken in [LZ17], is to explicitly study all the local equations. The other approach, which we take in the current paper, is to compute it using the Lefschetz trace formula. Thus we obtainProof. This follows immediately from Proposition 2.5.1.2.6. Review of regular elements. We recall the definition of regular elements and some standard facts. Let G be a reductive group over k.Definition 2.6.1. An element g ∈ G is called regular, if the centralizer G g of g in G has dimension equal to the rank of G. The set of regular elements is denoted by G reg .If G is semi-simple, the above definition is the same as [Ste65]. In general, one easily checks that g ∈ G is regular in the above sense if and only if the image of g in G ad is regular. Thus we can easily transport the results from [Ste65], which only discusses semi-simple groups, to reductive groups.Theorem 2.6.2. An element g ∈ G is regular if and only if there are only finitely many Borel subgroups of G that contain g.Proof. This follows from [Ste65, Theorem 1.1] applied to G ad .Proposition 2.6.3. Assume G ′ is a reductive group over k that contains G as a closed subgroup. ThenProof. Fix a Borel subgroup B ′ ⊂ G ′ that contains B. By Theorem 2.6.2, it suffices to show that the natural map between flag varie...